Method and apparatus for performing physical layer mobility procedures

ABSTRACT

Methods to perform, maintain and report measurements on a transmission-reception point (TRP) using limited reference signal transmission are described herein. The mobility measurement reports may utilize physical channels. Methods to obtain measurements on neighbor TRPs using limited RS transmissions are also described herein. Random-Access procedures to enable the addition of a neighbor TRP or handover without requiring higher layer signaling (and possibly without an interface between source and target TRP) are also described herein. New triggers to perform RA in order to decrease handover latency are also described herein. Wireless Transmit/Receive Unit (WTRU) behavior upon receiving RAR from multiple possible TRPs are also described herein. For example, a WTRU may store RAR information and use it later in an interrupted RA procedure.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.62/315,080, filed Mar. 30, 2016, and U.S. Provisional Application No.62/334,630, filed May 11, 2016, the contents of both of which are herebyincorporated herein by reference in their entirety.

BACKGROUND

Mobile communications are in continuous evolution and are already at thedoorstep of its fifth incarnation—5G. As with previous generations, newuse cases largely contributed in setting the requirements for the newsystem. It is expected that the 5G air interface will at least enablethe following use cases: (1) improved broadband performance (IBB); (2)industrial control and communications (ICC) and vehicular applications(V2X); and (3) Massive Machine-Type Communications (mMTC). The aboveuses cases are thus translated into many requirements for the 5Ginterface that should be balanced and optimized.

SUMMARY

To be Completed Once Claims are Finalized

A method and wireless transmit/receive unit (WTRU) for performinghandover among a plurality of coordinated transmission-reception points(TRPs) is disclosed. The method begins by measuring a first referencesignal (RS) of a first of the plurality of coordinated TRPs and a secondRS of a second of the plurality of coordinated TRPs. Then the WTRUreceives a grant to transmit to the coordinated TRPs. Next the WTRUtransmits to the first of the plurality of coordinated TRPs; anddetermines whether to transmit to the second of the plurality ofcoordinated TRPs rather than the first of the plurality of coordinatedTRPs, based on the first RS, the second RS, and a change incircumstances.

A method and WTRU for performing a random access procedure is alsodisclosed. The method begins by performing random access procedures to aplurality of coordinated TRPs using the same resources for each TRP.Then the WTRU receives at least one random access response (RAR). Basedon the received responses, the WTRU selects one random access responseof a particular TRP of the plurality of coordinated TRPs to continue therandom access procedure, and stores the contents of the remaining accessresponse. Then the WTRU continues the random access procedure with theparticular TRP.

BRIEF DESCRIPTION OF THE DRAWINGS

A more detailed understanding may be had from the following description,given by way of example in conjunction with the accompanying drawingswherein:

FIG. 1A is a system diagram of an example communications system in whichone or more disclosed embodiments may be implemented;

FIG. 1B is a system diagram of an example wireless transmit/receive unit(WTRU) that may be used within the communications system illustrated inFIG. 1A;

FIG. 1C is a system diagram of an example radio access network and anexample core network that may be used within the communications systemillustrated in FIG. 1A;

FIG. 2 is a block diagram of an example of different transmissionbandwidths;

FIG. 3 is a block diagram of a system bandwidth utilizing a flexiblespectrum allocation;

FIG. 4 is a block diagram of a frame structure and timing relationshipsfor TDD duplexing;

FIG. 5 is a block diagram of a frame structure and timing relationshipsfor TDD duplexing;

FIG. 6 shows a flow diagram of a mobility process; and

FIG. 7A through FIG. 7D are diagrams of an architecture of TRP mobilityin different steps in a mobility process.

DETAILED DESCRIPTION

FIG. 1A is a diagram of an example communications system 100 in whichone or more disclosed embodiments may be implemented. The communicationssystem 100 may be a multiple access system that provides content, suchas voice, data, video, messaging, broadcast, etc., to multiple wirelessusers. The communications system 100 may enable multiple wireless usersto access such content through the sharing of system resources,including wireless bandwidth. For example, the communications systems100 may employ one or more channel access methods, such as code divisionmultiple access (CDMA), time division multiple access (TDMA), frequencydivision multiple access (FDMA), orthogonal FDMA (OFDMA), single-carrierFDMA (SC-FDMA), and the like.

As shown in FIG. 1A, the communications system 100 may include wirelesstransmit/receive units (WTRUs) 102 a, 102 b, 102 c, 102 d, a radioaccess network (RAN) 104, a core network 106, a public switchedtelephone network (PSTN) 108, the Internet 110, and other networks 112,though it will be appreciated that the disclosed embodiments contemplateany number of WTRUs, base stations, networks, and/or network elements.Each of the WTRUs 102 a, 102 b, 102 c, 102 d may be any type of deviceconfigured to operate and/or communicate in a wireless environment. Byway of example, the WTRUs 102 a, 102 b, 102 c, 102 d may be configuredto transmit and/or receive wireless signals and may include userequipment (UE), a mobile station, a fixed or mobile subscriber unit, apager, a cellular telephone, a personal digital assistant (PDA), asmartphone, a laptop, a netbook, a personal computer, a wireless sensor,consumer electronics, and the like.

The communications systems 100 may also include a base station 114 a anda base station 114 b. Each of the base stations 114 a, 114 b may be anytype of device configured to wirelessly interface with at least one ofthe WTRUs 102 a, 102 b, 102 c, 102 d to facilitate access to one or morecommunication networks, such as the core network 106, the Internet 110,and/or the other networks 112. By way of example, the base stations 114a, 114 b may be a base transceiver station (BTS), a Node-B, an eNode B,a Home Node B, a Home eNode B, a site controller, an access point (AP),a wireless router, and the like. While the base stations 114 a, 114 bare each depicted as a single element, it will be appreciated that thebase stations 114 a, 114 b may include any number of interconnected basestations and/or network elements.

The base station 114 a may be part of the RAN 104, which may alsoinclude other base stations and/or network elements (not shown), such asa base station controller (BSC), a radio network controller (RNC), relaynodes, etc. The base station 114 a and/or the base station 114 b may beconfigured to transmit and/or receive wireless signals within aparticular geographic region, which may be referred to as a cell (notshown). The cell may further be divided into cell sectors. For example,the cell associated with the base station 114 a may be divided intothree sectors. Thus, in one embodiment, the base station 114 a mayinclude three transceivers, i.e., one for each sector of the cell. Inanother embodiment, the base station 114 a may employ multiple-inputmultiple-output (MIMO) technology and, therefore, may utilize multipletransceivers for each sector of the cell.

The base stations 114 a, 114 b may communicate with one or more of theWTRUs 102 a, 102 b, 102 c, 102 d over an air interface 116, which may beany suitable wireless communication link (e.g., radio frequency (RF),microwave, infrared (IR), ultraviolet (UV), visible light, etc.). Theair interface 116 may be established using any suitable radio accesstechnology (RAT).

More specifically, as noted above, the communications system 100 may bea multiple access system and may employ one or more channel accessschemes, such as CDMA, TDMA, FDMA, OFDMA, SC-FDMA, and the like. Forexample, the base station 114 a in the RAN 104 and the WTRUs 102 a, 102b, 102 c may implement a radio technology such as Universal MobileTelecommunications System (UMTS) Terrestrial Radio Access (UTRA), whichmay establish the air interface 116 using wideband CDMA (WCDMA). WCDMAmay include communication protocols such as High-Speed Packet Access(HSPA) and/or Evolved HSPA (HSPA+). HSPA may include High-Speed DownlinkPacket Access (HSDPA) and/or High-Speed Uplink Packet Access (HSUPA).

In another embodiment, the base station 114 a and the WTRUs 102 a, 102b, 102 c may implement a radio technology such as Evolved UMTSTerrestrial Radio Access (E-UTRA), which may establish the air interface116 using Long Term Evolution (LTE) and/or LTE-Advanced (LTE-A).

In other embodiments, the base station 114 a and the WTRUs 102 a, 102 b,102 c may implement radio technologies such as IEEE 802.16 (i.e.,Worldwide Interoperability for Microwave Access (WiMAX)), CDMA2000,CDMA2000 1X, CDMA2000 EV-DO, Interim Standard 2000 (IS-2000), InterimStandard 95 (IS-95), Interim Standard 856 (IS-856), Global System forMobile communications (GSM), Enhanced Data rates for GSM Evolution(EDGE), GSM EDGE (GERAN), and the like.

The base station 114 b in FIG. 1A may be a wireless router, Home Node B,Home eNode B, or access point, for example, and may utilize any suitableRAT for facilitating wireless connectivity in a localized area, such asa place of business, a home, a vehicle, a campus, and the like. In oneembodiment, the base station 114 b and the WTRUs 102 c, 102 d mayimplement a radio technology such as IEEE 802.11 to establish a wirelesslocal area network (WLAN). In another embodiment, the base station 114 band the WTRUs 102 c, 102 d may implement a radio technology such as IEEE802.15 to establish a wireless personal area network (WPAN). In yetanother embodiment, the base station 114 b and the WTRUs 102 c, 102 dmay utilize a cellular-based RAT (e.g., WCDMA, CDMA2000, GSM, LTE,LTE-A, etc.) to establish a picocell or femtocell. As shown in FIG. 1A,the base station 114 b may have a direct connection to the Internet 110.Thus, the base station 114 b may not be required to access the Internet110 via the core network 106.

The RAN 104 may be in communication with the core network 106, which maybe any type of network configured to provide voice, data, applications,and/or voice over internet protocol (VoIP) services to one or more ofthe WTRUs 102 a, 102 b, 102 c, 102 d. For example, the core network 106may provide call control, billing services, mobile location-basedservices, pre-paid calling, Internet connectivity, video distribution,etc., and/or perform high-level security functions, such as userauthentication. Although not shown in FIG. 1A, it will be appreciatedthat the RAN 104 and/or the core network 106 may be in direct orindirect communication with other RANs that employ the same RAT as theRAN 104 or a different RAT. For example, in addition to being connectedto the RAN 104, which may be utilizing an E-UTRA radio technology, thecore network 106 may also be in communication with another RAN (notshown) employing a GSM radio technology.

The core network 106 may also serve as a gateway for the WTRUs 102 a,102 b, 102 c, 102 d to access the PSTN 108, the Internet 110, and/orother networks 112. The PSTN 108 may include circuit-switched telephonenetworks that provide plain old telephone service (POTS). The Internet110 may include a global system of interconnected computer networks anddevices that use common communication protocols, such as thetransmission control protocol (TCP), user datagram protocol (UDP) andthe internet protocol (IP) in the TCP/IP internet protocol suite. Thenetworks 112 may include wired or wireless communications networks ownedand/or operated by other service providers. For example, the networks112 may include another core network connected to one or more RANs,which may employ the same RAT as the RAN 104 or a different RAT.

Some or all of the WTRUs 102 a, 102 b, 102 c, 102 d in thecommunications system 100 may include multi-mode capabilities, i.e., theWTRUs 102 a, 102 b, 102 c, 102 d may include multiple transceivers forcommunicating with different wireless networks over different wirelesslinks. For example, the WTRU 102 c shown in FIG. 1A may be configured tocommunicate with the base station 114 a, which may employ acellular-based radio technology, and with the base station 114 b, whichmay employ an IEEE 802 radio technology.

FIG. 1B is a system diagram of an example WTRU 102. As shown in FIG. 1B,the WTRU 102 may include a processor 118, a transceiver 120, atransmit/receive element 122, a speaker/microphone 124, a keypad 126, adisplay/touchpad 128, non-removable memory 130, removable memory 132, apower source 134, a global positioning system (GPS) chipset 136, andother peripherals 138. It will be appreciated that the WTRU 102 mayinclude any sub-combination of the foregoing elements while remainingconsistent with an embodiment.

The processor 118 may be a general purpose processor, a special purposeprocessor, a conventional processor, a digital signal processor (DSP), aplurality of microprocessors, one or more microprocessors in associationwith a DSP core, a controller, a microcontroller, Application SpecificIntegrated Circuits (ASICs), Field Programmable Gate Array (FPGAs)circuits, any other type of integrated circuit (IC), a state machine,and the like. The processor 118 may perform signal coding, dataprocessing, power control, input/output processing, and/or any otherfunctionality that enables the WTRU 102 to operate in a wirelessenvironment. The processor 118 may be coupled to the transceiver 120,which may be coupled to the transmit/receive element 122. While FIG. 1Bdepicts the processor 118 and the transceiver 120 as separatecomponents, it will be appreciated that the processor 118 and thetransceiver 120 may be integrated together in an electronic package orchip.

The transmit/receive element 122 may be configured to transmit signalsto, or receive signals from, a base station (e.g., the base station 114a) over the air interface 116. For example, in one embodiment, thetransmit/receive element 122 may be an antenna configured to transmitand/or receive RF signals. In another embodiment, the transmit/receiveelement 122 may be an emitter/detector configured to transmit and/orreceive IR, UV, or visible light signals, for example. In yet anotherembodiment, the transmit/receive element 122 may be configured totransmit and receive both RF and light signals. It will be appreciatedthat the transmit/receive element 122 may be configured to transmitand/or receive any combination of wireless signals.

In addition, although the transmit/receive element 122 is depicted inFIG. 1B as a single element, the WTRU 102 may include any number oftransmit/receive elements 122. More specifically, the WTRU 102 mayemploy MIMO technology. Thus, in one embodiment, the WTRU 102 mayinclude two or more transmit/receive elements 122 (e.g., multipleantennas) for transmitting and receiving wireless signals over the airinterface 116.

The transceiver 120 may be configured to modulate the signals that areto be transmitted by the transmit/receive element 122 and to demodulatethe signals that are received by the transmit/receive element 122. Asnoted above, the WTRU 102 may have multi-mode capabilities. Thus, thetransceiver 120 may include multiple transceivers for enabling the WTRU102 to communicate via multiple RATs, such as UTRA and IEEE 802.11, forexample.

The processor 118 of the WTRU 102 may be coupled to, and may receiveuser input data from, the speaker/microphone 124, the keypad 126, and/orthe display/touchpad 128 (e.g., a liquid crystal display (LCD) displayunit or organic light-emitting diode (OLED) display unit). The processor118 may also output user data to the speaker/microphone 124, the keypad126, and/or the display/touchpad 128. In addition, the processor 118 mayaccess information from, and store data in, any type of suitable memory,such as the non-removable memory 130 and/or the removable memory 132.The non-removable memory 130 may include random-access memory (RAM),read-only memory (ROM), a hard disk, or any other type of memory storagedevice. The removable memory 132 may include a subscriber identitymodule (SIM) card, a memory stick, a secure digital (SD) memory card,and the like. In other embodiments, the processor 118 may accessinformation from, and store data in, memory that is not physicallylocated on the WTRU 102, such as on a server or a home computer (notshown).

The processor 118 may receive power from the power source 134, and maybe configured to distribute and/or control the power to the othercomponents in the WTRU 102. The power source 134 may be any suitabledevice for powering the WTRU 102. For example, the power source 134 mayinclude one or more dry cell batteries (e.g., nickel-cadmium (NiCd),nickel-zinc (NiZn), nickel metal hydride (NiMH), lithium-ion (Li-ion),etc.), solar cells, fuel cells, and the like.

The processor 118 may also be coupled to the GPS chipset 136, which maybe configured to provide location information (e.g., longitude andlatitude) regarding the current location of the WTRU 102. In additionto, or in lieu of, the information from the GPS chipset 136, the WTRU102 may receive location information over the air interface 116 from abase station (e.g., base stations 114 a, 114 b) and/or determine itslocation based on the timing of the signals being received from two ormore nearby base stations. It will be appreciated that the WTRU 102 mayacquire location information by way of any suitablelocation-determination method while remaining consistent with anembodiment.

The processor 118 may further be coupled to other peripherals 138, whichmay include one or more software and/or hardware modules that provideadditional features, functionality and/or wired or wirelessconnectivity. For example, the peripherals 138 may include anaccelerometer, an e-compass, a satellite transceiver, a digital camera(for photographs or video), a universal serial bus (USB) port, avibration device, a television transceiver, a hands free headset, aBluetooth® module, a frequency modulated (FM) radio unit, a digitalmusic player, a media player, a video game player module, an Internetbrowser, and the like.

FIG. 1C is a system diagram of the RAN 104 and the core network 106according to an embodiment. As noted above, the RAN 104 may employ anE-UTRA radio technology to communicate with the WTRUs 102 a, 102 b, 102c over the air interface 116. The RAN 104 may also be in communicationwith the core network 106.

The RAN 104 may include eNode-Bs 140 a, 140 b, 140 c, though it will beappreciated that the RAN 104 may include any number of eNode-Bs whileremaining consistent with an embodiment. The eNode-Bs 140 a, 140 b, 140c may each include one or more transceivers for communicating with theWTRUs 102 a, 102 b, 102 c over the air interface 116. In one embodiment,the eNode-Bs 140 a, 140 b, 140 c may implement MIMO technology. Thus,the eNode-B 140 a, for example, may use multiple antennas to transmitwireless signals to, and receive wireless signals from, the WTRU 102 a.

Each of the eNode-Bs 140 a, 140 b, 140 c may be associated with aparticular cell (not shown) and may be configured to handle radioresource management decisions, handover decisions, scheduling of usersin the uplink and/or downlink, and the like. As shown in FIG. 1C, theeNode-Bs 140 a, 140 b, 140 c may communicate with one another over an X2interface.

The core network 106 shown in FIG. 1C may include a mobility managemententity gateway (MME) 142, a serving gateway 144, and a packet datanetwork (PDN) gateway 146. While each of the foregoing elements aredepicted as part of the core network 106, it will be appreciated thatany one of these elements may be owned and/or operated by an entityother than the core network operator.

The MME 142 may be connected to each of the eNode-Bs 140 a, 140 b, 140 cin the RAN 104 via an S1 interface and may serve as a control node. Forexample, the MME 142 may be responsible for authenticating users of theWTRUs 102 a, 102 b, 102 c, bearer activation/deactivation, selecting aparticular serving gateway during an initial attach of the WTRUs 102 a,102 b, 102 c, and the like. The MME 142 may also provide a control planefunction for switching between the RAN 104 and other RANs (not shown)that employ other radio technologies, such as GSM or WCDMA.

The serving gateway 144 may be connected to each of the eNode Bs 140 a,140 b, 140 c in the RAN 104 via the Si interface. The serving gateway144 may generally route and forward user data packets to/from the WTRUs102 a, 102 b, 102 c. The serving gateway 144 may also perform otherfunctions, such as anchoring user planes during inter-eNode B handovers,triggering paging when downlink data is available for the WTRUs 102 a,102 b, 102 c, managing and storing contexts of the WTRUs 102 a, 102 b,102 c, and the like.

The serving gateway 144 may also be connected to the PDN gateway 146,which may provide the WTRUs 102 a, 102 b, 102 c with access topacket-switched networks, such as the Internet 110, to facilitatecommunications between the WTRUs 102 a, 102 b, 102 c and IP-enableddevices.

The core network 106 may facilitate communications with other networks.For example, the core network 106 may provide the WTRUs 102 a, 102 b,102 c with access to circuit-switched networks, such as the PSTN 108, tofacilitate communications between the WTRUs 102 a, 102 b, 102 c andtraditional land-line communications devices. For example, the corenetwork 106 may include, or may communicate with, an IP gateway (e.g.,an IP multimedia subsystem (IMS) server) that serves as an interfacebetween the core network 106 and the PSTN 108. In addition, the corenetwork 106 may provide the WTRUs 102 a, 102 b, 102 c with access to thenetworks 112, which may include other wired or wireless networks thatare owned and/or operated by other service providers.

Other network 112 may further be connected to an IEEE 802.11 basedwireless local area network (WLAN) 160. The WLAN 160 may include anaccess router 165. The access router may contain gateway functionality.The access router 165 may be in communication with a plurality of accesspoints (APs) 170 a, 170 b. The communication between access router 165and APs 170 a, 170 b may be via wired Ethernet (IEEE 802.3 standards),or any type of wireless communication protocol. AP 170 a is in wirelesscommunication over an air interface with WTRU 102 d.

The following abbreviations and acronyms may be referred to herein:

-   -   Δf Sub-carrier spacing    -   5gFlex 5G Flexible Radio Access Technology    -   5gNB 5GFlex NodeB    -   ACK Acknowledgement    -   BLER Block Error Rate    -   BTI Basic TI (in integer multiple of one or more symbol        duration)    -   CB Contention-Based (e.g. access, channel, resource)    -   CoMP Coordinated Multi-Point transmission/reception    -   CP Cyclic Prefix    -   CP-OFDM Conventional OFDM (relying on cyclic prefix)    -   CQI Channel Quality Indicator    -   CN Core Network (e.g. LTE packet core)    -   CRC Cyclic Redundancy Check    -   CSI Channel State Information    -   D2D Device to Device transmissions (e.g. LTE Sidelink)    -   DCI Downlink Control Information    -   DL Downlink    -   DM-RS Demodulation Reference Signal    -   DRB Data Radio Bearer    -   EPC Evolved Packet Core    -   FBMC Filtered Band Multi-Carrier    -   FBMC/OQAM A FBMC technique using Offset Quadrature Amplitude        Modulation    -   FDD Frequency Division Duplexing    -   FDM Frequency Division Multiplexing    -   ICC Industrial Control and Communications    -   ICIC Inter-Cell Interference Cancellation    -   IP Internet Protocol    -   LAA License Assisted Access    -   LBT Listen-Before-Talk    -   LCH Logical Channel    -   LCP Logical Channel Prioritization    -   LTE Long Term Evolution e.g. from 3GPP LTE R8 and up    -   MAC Medium Access Control    -   NACK Negative ACK    -   MC MultiCarrier    -   MCS Modulation and Coding Scheme    -   MIMO Multiple Input Multiple Output    -   MTC Machine-Type Communications    -   NAS Non-Access Stratum    -   OFDM Orthogonal Frequency-Division Multiplexing    -   OOB Out-Of-Band (emissions)    -   P_(cmax) Total available WTRU power in a given TI    -   PHY Physical Layer    -   PRACH Physical Random Access Channel    -   PRB Physical Resource Block    -   PRG Precoding Resource Group    -   PDU Protocol Data Unit    -   PER Packet Error Rate    -   PLR Packet Loss Rate    -   PMI Precoding Matrix Indicator    -   PTI Precoding Type Indicator    -   QoS Quality of Service (from the physical layer perspective)    -   RAB Radio Access Bearer    -   RACH Random Access Channel (or procedure)    -   RF Radio Front end    -   RNTI Radio Network Identifier    -   RRC Radio Resource Control    -   RRM Radio Resource Management    -   RS Reference Signal    -   RTT Round-Trip Time    -   SCMA Single Carrier Multiple Access    -   SDU Service Data Unit    -   SOM Spectrum Operation Mode    -   SS Synchronization Signal    -   SRB Signalling Radio Bearer    -   SWG Switching Gap (in a self-contained subframe)    -   TB Transport Block    -   TDD Time-Division Duplexing    -   TDM Time-Division Multiplexing    -   TI Time Interval (in integer multiple of one or more BTI)    -   TTI Transmission Time Interval (in integer multiple of one or        more TI)    -   TRx Transceiver    -   UFMC Universal Filtered MultiCarrier    -   UF-OFDM Universal Filtered OFDM    -   UL Uplink    -   V2V Vehicle to vehicle communications    -   V2X Vehicular communications    -   WLAN Wireless Local Area Networks and related technologies (IEEE        802.xx domain)

In LTE a WTRU may be configured to perform higher-layer measurementsthat may enable mobility. A WTRU may perform measurements on acell-specific reference signal (CRS), either in a discovery referencesignal (DRS) or transmitted periodically. Furthermore, the WTRU mayperform measurements on symbols within a DRS or symbols of a CRS. A WTRUmay be configured to obtain measurements and to report the results.

A WTRU may be configured to report measurements on the basis of one ormore measurement based trigger. A WTRU may be configured to obtain andreport a Reference Signal Received Power (RSRP) measurement. To obtainthe RSRP, the WTRU measures the received power on a CRS. A WTRU may alsobe configured to obtain and report a CSI-RSRP measurement. To obtain aCSI-RSRP, the WTRU may be configured to measure received power on aCSI-RS resource. A WTRU may be configured to obtain and report aReference Signal Strength Indicator (RSSI) measurement. The RSSI may bea measure of total power observed on a complete symbol. The completesymbol may be a symbol with CRS, or may be all symbols of a subframecontaining CRS. A WTRU may be configured to obtain and report aReference Signal Received Quality (RSRQ) measurement. The RSRQ may beobtained as a function of RSRP and RSSI measurement. If the RSRQ is afunction of RSRP and RSSI, RSSI would serve as a proxy to determine anamount of average interference on a frequency.

In LTE, a WTRU may blindly detect PSS/SSS to determine the presence of acell. From the PSS/SSS a WTRU may acquire frequency and symbolsynchronization of a cell, acquire frame timing of a cell and determinethe physical-layer cell identity. Based on the physical-layer cellidentity, the WTRU may determine a CRS configuration. The CRS enablesthe WTRU to perform measurements on a cell and also to demodulatetransmissions from the cell.

A WTRU may also acquire system information from a cell. Systeminformation can be split up into parts, which may include theMaster-Information Block (MIB) and System-Information Blocks (SIBs). TheMIB may be transmitted using a broadcast channel (BCH). SIBs may betransmitted using a downlink shared channel (DL-SCH).

From the MIB, a WTRU may determine information about the cell's DLbandwidth, information about a PHICH configuration and a System FrameNumber (SFN). From SIBs, a WTRU may determine whether it can access acell. The WTRU may also obtain information to access the cell from theSIBs. Information to access the cell may include UL cell bandwidth,random-access parameters and parameters related to UL power control.

A WTRU may perform Random Acces (RA) to a cell for different purposes.RA may be used for initial access, such as when establishing a radiolink to the cell. RA may also be used to re-establish a radio link withthe cell after an initial link fails RA may also be used to establish ULsynchronization, or for handover, when UL synchronization is needed. RAmay also be used for positioning, or RA may be used as a schedulingrequest.

Random Access may be performed by a WTRU, which would begin an RAsession by transmitting a preamble on PRACH resources to a cell. Thecell may detect the preamble transmission. If so, the cell transmits aRandom-access Response (RAR). A RAR may contain an index of an RApreamble, the network detected, a timing correction, a scheduling grantto be used by the WTRU , and a temporary identity for furthercommunication between the WTRU and the network. The WTRU then transmitsthe necessary messages to the eNB using UL-SCH resources assigned in theRAR. UL-SCH resources may include a terminal identity, which may be usedto enable contention-resolution, which may be required. Contentionresolution would then occur, which may include sending a message onPDCCH using a WTRU's identity, or may include DL-SCH with a terminalidentity.

A 5G air interface may require support for improved broadbandperformance (IBB) over previous generation networks. A 5G air interfacemay also require support for Industrial Control and Communications (ICC)or Vehicular Applications (V2X). A 5G air interface may also be expectedto support Massive Machine-Type Communications (mMTC).

A 5G interface may also require support for baseband filtering offrequency-domain waveform. In designing an interface for this potentialrequirement, it may be beneficial for baseband filtering of thefrequency-domain waveform to have the ability to enable effectiveaggregation of up to 150-200 MHz total spectrum within a given RFtransceiver path without relying on a re-design of the front end of theinterface.

a 5G interface may be implemented using spectrum across widely separatedoperating bands (e.g. 900 MHz and 3.5 GHz), which may require multipleRF transceiver chains. These may be necessary because of antenna sizerequirements and amplifier optimization design constraints which may bedifferent across different operating bands. This could result in a needfor multiple antennae within a WTRU device. For example, a WTRU designedto operate in 5G networks at different frequencies may require threeseparate RF transceiver paths: for example, one below 1 GHz, a anotherfor the 1.8-3.5 GHz frequency range and a another covering the 4-6 GHzfrequency range. Native built-in support for Massive MIMO antennaconfigurations is an important second order requirement as well.

5G systems may also support ultra-low transmission latency, such as, airinterface latency as low as 1 ms RTT. A latency requirement such as thismay require support for TTIs between 100 us and 250 us. Additionally,support for ultra-low access latency, which is time from initial systemaccess until the completion of the transmission of the first user planedata unit, may also be required or desired. For example, an end-to-end(e2e) latency of less than 10 ms may be required.

5G systems may also support transmission reliability that is lower,perhaps substantially lower, than what is possible with LTE systems.99.999% transmission success and service availability may be required ordesired. Support for mobility for speed in the range of 0-500 km/h mayalso be required, as may reduced Packet Loss Rate, such as a rate ofless than 10e⁻⁶.

5G systems may also support MTC operation (including narrowbandoperation). A 5G network may also support narrowband operation, forexample, using less than 200 KHz) Extended battery life, perhapsextending years, may also be supported. Reducing communication overheadfor small and infrequent data transmissions may also be supported,potentially including low data rate in the range of 1-100 kbps, withaccess latency of seconds to hours.

mMTC may require the system to support narrowband operation. Theresulting link budget should be comparable to that of LTE extendedcoverage, but the system will support a very large number of MTCdevices, potentially up to 200,000 devices per square kilometer, withoutadverse impact on spectral efficiency for other supported services.

The above set of requirements can be met by designing the 5G network inaccordance with design features as described herein. For example, a 5Gsystem may be designed to enable flexible spectrum usage, deploymentstrategies and operation. The system may be designed to support spectrumof varying size, perhaps using multiple frequency ranges simultaneouslyor in rapid succession, and may include use of multiple carrier networksthat may be in the same and/or in different frequency bands, and may belicensed, unlicensed or a mixture of both. The system may also supportnarrowband and wideband operation, different duplexing methods,dynamically variable DL/UL allocation, variable TTI lengths, scheduledand unscheduled transmissions, synchronous and asynchronoustransmissions, separation of user plane from the control plane, andmulti-node connectivity.

A 5G system may also be designed to integrate with legacy (E−) UTRAN andEPC/CN aspects. Although the system may not require backwardcompatibility, the system may be required to integrate and/orinteroperate with the legacy interfaces, or evolutions of legacyinterfaces, which may include legacy CN, such as the S1 interface orNAS, and eNBs such as an X2 interface and dual connectivity with LTE.The system may also be required to enable legacy aspects of priorgeneration networks, such as support for existing QoS and securitymechanisms.

Some elements of the 5G design could be retrofitted in LTE Evolution,which would allow for backward compatibility of some or all components.For example, TTIs shorter than a 0.5 ms LTE slot, using a differentwaveform to enable ultra-low latency, may be used. Support forD2D/Sidelink operation may also be implemented. Support for LAAoperation using LBT; and Support for relaying may also be implemented.

OFDM is the basic signal format for data transmissions in both LTE andin IEEE 802.11 networks. OFDM efficiently divides the spectrum intomultiple parallel orthogonal subbands. Each subcarrier is shaped using arectangular window in the time domain, leading to sinc-shapedsubcarriers in the frequency domain. Because of this, OFDMA requiresperfect frequency synchronization and tight management of uplink timingalignment within the cyclic prefix, which maintains orthogonalitybetween signals and minimize intercarrier interference. This kind oftight synchronization may not be well-suited in a system where a WTRU isconnected to multiple access points simultaneously. Additional powerreduction may also be applied to uplink transmissions for compliancewith spectral emission requirements to adjacent bands, which may behelpful in dealing with fragmented spectrum for the WTRU'stransmissions.

Some of the shortcomings of conventional OFDM (CP-OFDM) may be addressedby more stringent RF requirements for implementations, which may behelpful when operating using a large amount of contiguous spectrum notrequiring aggregation. A CP-based OFDM transmission scheme could alsolead to a downlink physical layer for 5G, which would be similar to thatof legacy systems, perhaps changed mainly with respect to pilot signaldensity and location.

Because of the differences in needs and use cases between a new 5Gnetwork and legacy systems, including fragmented spectrum allocation, a5gFLEX design focuses on other waveform candidates. However,conventional OFDM remains a possible candidate for 5G systems, at leastfor the downlink transmission scheme. Building upon OFDMA and legacy LTEsystems, a design for flexible radio access for 5G is proposed herein.

A 5gFLEX downlink transmission scheme is based on a multicarrierwaveform characterized by high spectral containment with lower sidelobes and lower OOB emissions. Possible MC waveform candidates for 5Ginclude OFDM-OQAM and UFMC (UF-OFDM).

Multicarrier modulation waveforms may divide a channel into subchannelsand modulate data symbols on subcarriers in these subchannels. WithOFDM-OQAM, a filter may be applied in the time domain per subcarrier tothe OFDM signal, to reduce OOB. OFDM-OQAM causes low interference toadjacent bands, does not need large guard bands, and does not require acyclic prefix. However, OFDM-OQAM is sensitive to multipath effects andto high delay spread in terms of orthogonality thereby complicatingequalization and channel estimation.

With UFMC (UF-OFDM), a filter may also be applied to the OFDM signal inthe time domain, to reduce OOB. Filtering is applied per subband to usespectrum fragments, thereby reducing complexity. However, if there areunused spectrum fragments in the band, OOB emissions in these fragmentswill remain as high as for conventional OFDM. In other words, UF-OFDMimproves over OFDM only at the edges of the filtered spectrum.Improvements are not seen in the spectral hole.

Methods described herein are not limited to the above waveforms and maybe applicable to other waveforms. The waveforms described above will befurther used herein, with the understanding that they are examples only.Such waveforms may enable multiplexing in frequency of signals withnon-orthogonal characteristics, such as different subcarrier spacing,and co-existence of asynchronous signals without requiring complexinterference cancellation receivers. The methods may also facilitate theaggregation of fragmented pieces of spectrum in the baseband processingas a lower cost alternative to their implementation as part of RFprocessing.

Different waveforms co-existing within the same band may be considered,for example support for mMTC narrowband operation using SCMA may beconsidered. Another example of different waveforms co-existing in thesame band may be the support, within the same band, of a combination ofdifferent waveforms, perhaps including CP-OFDM, OFDM-OQAM and UF-OFDM,for all aspects and for both downlink and uplink transmissions. Thisco-existence may include transmissions using different types ofwaveforms between different WTRUs, or transmissions from the same WTRUeither simultaneously with some overlap, or consecutive in the timedomain.

Other ways to improve co-existence may include support for hybrid typesof waveforms, including waveforms and/or transmissions that support atleast one of a possibly varying CP duration, for example from onetransmission to another. A combination of a CP and a low power tail(e.g. a zero tail) may also improve co-existence. A form of hybrid guardinterval may improve co-existence, and may include using a low power CPand an adaptive low power tail. Similar improvements may also be used.Waveforms may support dynamic variation and/or control of further designoptions, which may include filtering options such as whether filteringis applied at the edge of the spectrum used for reception of anytransmissions for a given carrier frequency, at the edge of a spectrumused for reception of a transmission associated to a specific SOM, orper subband, or per group thereof. An uplink transmission scheme may usea same or different waveform as for downlink transmissions. Multiplexingof transmissions to and from different WTRUs in the same cell may bebased on FDMA and TDMA.

5gFLEX radio access design may be characterized by spectrum flexibility,which enables deployment in different frequency bands with differentcharacteristics, including different duplex arrangements. Differentand/or variable sizes of the available spectrum, including contiguousand non-contiguous spectrum allocations in the same or different bands,may also be used. Radio access design may also support variable timingaspects, including support for multiple TTI lengths and support forasynchronous transmissions.

TDD and/or FDD duplexing schemes may be supported. For FDD operation,supplemental downlink operation may be supported using spectrumaggregation. FDD operation may support full-duplex FDD, half-duplex FDDoperation, or both. For TDD operation, the DL/UL allocation is dynamicand is not based on a fixed DL/UL frame configuration. The length of aDL or a UL transmission interval may be set on a per transmissionopportunity basis.

In FIG. 2 an example of different transmission bandwidths is shown.5gFLEX design may allow for the possibility of different transmissionbandwidths on uplink, downlink, or both. Bandwidth may range fromnominal system bandwidth 201, shown in FIG. 2 as 5 MHz, up to the systembandwidth 202, shown as 20 Mhz. Three examples of UE channel bandwidthare shown, with UEx channel bandwidth 203 shown at 10 MHz, UEy channelbandwidth 204 shown at 20 MHz, and UEz channel bandwidth 205 shown at 5MHz. Other UE channel bandwidths may also be used between nominalbandwidth 201 and system bandwidth 202.

For single carrier operation, the supported system bandwidths 202 mayinclude at least 5, 10, 20, 40 and 80 MHz. Supported system bandwidthsmay be any bandwidth within a range, which can be from a few MHz up to160 MHz. Nominal bandwidths 201 could have one or more fixed possiblevalues. Narrowband transmissions of up to 200 KHz may be supportedwithin the operating bandwidth for MTC devices.

System bandwidth 202 herein may refer to the largest portion of spectrumthat can be managed by the network for a carrier. For the carrier, theportion that a WTRU minimally supports for cell acquisition,measurements and initial access to the network may correspond to thenominal system bandwidth 201. The WTRU may be configured with a channelbandwidth 203, 204, or 205 that is within the range of the entire systembandwidth 202. The WTRU's configured channel bandwidth may or may notinclude the nominal part of the system bandwidth as shown in FIG. 2,where UEx channel bandwidth 203 and UEy channel bandwidth 204 includethe nominal part of the system bandwidth 201, but UEz channel bandwidth205 uses a different 5 MHz band than the 5 MHz of the nominal systembandwidth 201.

Bandwidth flexibility can be achieved, because all applicable sets of RFrequirements, for a given maximum operating bandwidth in a band, can bemet without introducing additional allowed channel bandwidths for thatoperating band. Efficient support of baseband filtering of the frequencydomain waveform assists in achieving bandwidth flexibility.

A 5gFLEX physical layer may be band-agnostic and may support operationin licensed bands below 5 GHz and/or unlicensed bands in the range of5-6 GHz. For operation in unlicensed bands, LBT Cat 4 based channelaccess framework similar, to LTE LAA, may be supported.

Flexible Spectrum Allocation may be achieved. Downlink control channelsand signals may support FDM operation. A WTRU may acquire a downlinkcarrier by receiving transmissions using only the nominal part of thesystem bandwidth. For example, the WTRU may not initially need toreceive transmissions covering the entire bandwidth that is beingmanaged by the network for a particular carrier.

Downlink data channels may be allocated over a bandwidth that may or maynot correspond to the nominal system bandwidth, without restrictionsother than being within the WTRU's configured channel bandwidth. Forexample, the network may operate a carrier with a 12 MHz systembandwidth using a 5 MHz nominal bandwidth. This would allow WTRUs thatonly support 5 MHz maximum RF bandwidth to acquire and access thesystem, but also allocate +10 to −10 MHz of the carrier frequency toother WTRU's supporting up to 20 MHz worth of channel bandwidth.

FIG. 3 is an example of a spectrum allocation where differentsubcarriers with subcarrier spacing 306 may be at least conceptuallyassigned to different modes of operation (also known as SpectrumOperation Modes, hereafter SOM). Different SOM may be used to fulfilldifferent requirements for different transmission characteristics 307. ASOM may be defined by a subcarrier spacing 306, with examples shown assubcarrier spacing F₁ 308 and subcarrier spacing F₂ 309. A SOM may alsobe defined by a TTI length. A SOM may also be defined by one or morereliability features, which may include HARQ processing or a secondarycontrol channel. In some cases, a SOM may be used to refer to a specificwaveform or may be related to a processing feature, which may be used insupport of co-existence of different waveforms in the same carrier usingFDM and/or TDM. Processing features may also be used when coexistence ofFDD operation in a TDD band is supported, which may be in a TDM manneror a similar manner. Variable transmission characteristics 307 may alsobe used within the nominal system bandwidth 301 and/or the systembandwidth 302.

A single carrier operation may support spectrum aggregation, whereby theWTRU supports transmission and reception of multiple transport blocksover contiguous or non-contiguous sets physical resource blocks (PRBs)within the same operating band. Mapping of a single transport block toseparate sets of PRBs may also be used to achieve support for spectrumaggregation.

Multicarrier operation may also be supported using contiguous ornon-contiguous spectrum blocks within the same operating band, or acrosstwo or more operating bands. Aggregation of spectrum blocks usingdifferent modes such as FDD and TDD, or using different channel accessmethods i.e. licensed and unlicensed band operation below 6 GHz issupported.

Methods that configure, reconfigure and/or dynamically change the WTRU'smulticarrier aggregation may be helpful in supporting aggregation of thefrequency bands for multiple carriers in a single WTRU. FlexibleFraming, Timing, and Synchronization may be one manner of dynamicreconfiguration.

Examples of frame structure for Flexible Framing, Timing andSynchronization are shown in FIG. 4, for TDD and FIG. 5 for FDD.Downlink and uplink transmissions may be organized into radio frames410/510, which are characterized by fixed characteristics, such aslocation of downlink control information, and/or characteristics thatvary, such as transmission timing or supported types of transmissions.

Basic time interval (BTI) 411/511 is expressed in terms of an integernumber of one or more symbols, the duration of which may be a functionof subcarrier spacing applicable to a time-frequency resource. For FDD,subcarrier spacing may differ between uplink carrier frequency f_(UL)and downlink carrier frequency f_(DL) for a given frame, as shown inFIG. 5. As shown in FIG. 4 for TDD, f_(UL) and f_(DL) could use the sameor a combined subcarrier spacing as shown at f_(UL+DL) . . .

A transmission time interval (TTI) is the minimum time supported by thesystem between consecutive transmissions, where each would be associatedto different transport blocks (TBs), TTIDL for the downlink, and UL TRxfor the uplink. Consecutive transmissions may exclude a preamble, andmay include downlink control information (DCI) uplink controlinformation UCI. A TTI may be expressed in terms of an integerreflecting a number of one of more BTI(s) 411/511. A BTI 411/511 may bespecific to, or associated with, a given SOM.

The method may support frame durations that may be expressed asmicroseconds or miliseconds, and may include 100 us, 125 us (aka ⅛ ms),or 142.85 us (aka 1/7 ms, which is 2 nCP LTE OFDM symbols). The methodmay also support a frame duration of 1 ms to enable alignment with thelegacy LTE timing structure.

Each frame may start with downlink control information (DCI) of a fixedtime duration TDCI, which may precede downlink data transmission (DLTRx) for the carrier frequency: f_(UL+DL) for TDD and f_(DL) for FDD.

For TDD duplexing, a frame may comprise a downlink portion (DCI and DLTRx) and may also include an uplink portion (UL TRx) 219. A switchinggap (SWG) may precede the uplink portion of the frame.

For FDD duplexing only, a frame may comprise a downlink reference TTIand one or more TTI(s) for the uplink. The start of an uplink TTI may bederived using an offset (t_(offset)) which may be applied from the startof the downlink reference frame that overlaps with the start of theuplink frame.

For TDD, a 5gFLEX network may support D2D/V2x/Sidelink operation inframes, by including respective downlink control and forward directiontransmission. Downlink control and forward direction transition may bepresent in the DCI+DL TRx portion if a semi-static allocation of therespective resources is used. It may only be present in the DL TRxportion if dynamic allocation is used. Frames may also include therespective reverse direction transmission in the UL TRx portion.

For FDD, a 5gFLEX network may support D2D/V2x/Sidelink operation in theUL TRx portion of the frame by including respective downlink control,forward direction and reverse direction transmissions in the UL TRxportion, dynamic allocation of the respective resources may be used.

A scheduling function may be supported in the MAC layer. A network-basedscheduling mode may be supported, which may be useful for tightscheduling in terms of resources, timing, and transmission parameters ofdownlink transmissions and/or uplink transmissions. A WTRU-basedscheduling mode may be supported, which may be useful if moreflexibility, in terms of timing and transmission parameters, is desired.For both modes, scheduling information may be valid for a single TTI orfor multiple TTIs.

Network-based scheduling may enable the network to manage availableradio resources assigned to different WTRUs. This may help to optimizethe sharing of such resources. Dynamic scheduling may also be supported.

WTRU-based scheduling may enable the WTRU to opportunistically accessuplink resources with reduced latency on a per-need basis within a setof shared or dedicated uplink resources. These uplink resources may beassigned by the network either dynamically or statically. Synchronizedopportunistic transmissions, and unsynchronized opportunistictransmissions, or both, may be are supported. Contention-basedtransmissions and contention-free transmissions may also be supported.

Support for opportunistic transmissions may be included. Opportunistictransmissions may be scheduled or unscheduled. Opportunistictransmissions may be helpful to substantially reduce latency and/or savepower, which may be helpful in meeting requirements of a 5G networkand/or the mMTC use case.

A 5gFLEX network may support Logical Channel Prioritization, which mayinclude the association of data available for transmission and availableresources for uplink transmissions. Multiplexing of data with differentQoS requirements within the same transport block may be supported.

A transmission may be encoded using a number of different encodingmethods for forward error correction and block coding, which may usedifferent encoding methods with different characteristics.

In one example, an encoding method may generate a sequence ofinformation units. Each information unit, or block, may beself-contained, so that an error in the transmission of a first blockmay not impair the ability of the receiver to decode a second blocksuccessfully. This may be useful if the second block is error-free,and/or if sufficient redundancy can be found in the second block, or ina different block for which at least a portion was successfully decoded.

Raptor/fountain codes may be used for encoding, whereby a transmissionmay consist of a sequence of N raptor codes. One or more such codes maybe mapped to one or more transmission “symbols” in time. A “symbol” cancorrespond to one or more sets of information bits, which may mean oneor more octets. Encoding using raptor/fountain codes may be used to addFEC to a transmission, whereby the transmission could use N+1 or N+2raptor codes (or symbols, assuming a one-to-one raptor code symbolrelationship) so that the transmission may be more resilient to the lossof one “symbol,” which may occur due to interference, or by puncturingcaused by another transmission overlapping in time.

Reference signals may include synchronization signals and cell specificreference signals. System information may include broadcast channels. 5Gsystems may need to operate with reduced periodic transmission ofreference signals and/or system information. Reduction of referencesignals and/or system information can have benefits, such as reducingover-all interference levels and/or reducing power consumption atTransmission-Reception Points (TRPs).

Furthermore, it may also be beneficial to reduce signaling overhead forgeneric WTRU functions, such as mobility. Increased densification ofTRPs may greatly affect mobility. However, continuing to use legacy WTRUbehavior for mobility could lead to overhead that would negate any gainsachievable by ultra-dense deployments of TRPs.

As such, there is a need for a framework enabling a WTRU to maintainconnectivity with sets of TRPs. Therefore, there is also a need forWTRUs and TRPs to determine which TRP, in a set of TRPs, is the optimalTRP to serve the WTRU. This need can be met with one or more methods toenable a WTRU to maintain measurements on multiple TRPs with reducedreference signal and system information transmission overhead, so thatthe optimal serving TRP can be efficiently determined, and re-determinedwhen appropriate. Furthermore, there is a need for a method to enableWTRUs to perform mobility between and within sets of TRPs, with reducedsignaling.

Methods are provided herein whereby a WTRU may perform mobility betweenand within sets of TRPs, without requiring higher-layer control planetransmissions, and with reduced interfacing between TRPs, which reducesover-all latency on the network during a mobility operation. The reducedlatency of mobility may create benefits for different scenarios such aseMBB, where lower latency in performing mobility ensures that more timeis devoted to high throughput transmission of data, and URLLC, wherelower latency in mobility can provide reliability by ensuring WTRUs arealways connected to optimal TRPs.

A TRP may include a network element, such as a cell, and/or a WTRUcapable of D2D transmission and/or reception. A TRP may also indicate aspecific parameter of a network element. For example, a TRP may indicatea beam on which a cell may transmit and/or receive. In another example,a TRP may indicate a set of resources or usage type (e.g. SOM, or eMBB,URLLC, mMTC).

FIG. 6 is a flow diagram of a process whereby a WTRU receives RSconfiguration information from a source TRP, which allows it to transmitto a target TRP. As shown in FIG. 6, RS configuration 601 is sent from aSource TRP to a WTRU. The RS configuration may relate to a group ofcoordinated TRPs. In block 602, the WTRU performs measurements using oneor more RS for one or more TRPs. Measurements may be of many types, andmay relate to the ability of the WTRU to transmit and/or receive toand/or from a serving TRP (for example the Source TRP) and/or anon-serving TRP (for example, a Target TRP). Specific types ofmeasurements are discussed below. In block 603, the WTRU determines thatat least one measurement meets a threshold. In block 604, the WTRUperforms random access with a target TRP, possibly using resourcesdetermined from the measured RS. In another example, in block 604, theWTRU performs random access with a target TRP, using pre-configured orpre-determined resources. The resources may be pre-configured orpre-determined from a previous indication from the source TRP or fromthe Target TRP.

In block 605, The WTRU receives a response with a grant of resources.Resources may be for UL transmission, DL transmission, or both, or maybe for some other process or procedure. In block 606, the WTRU indicatesits own identity, which may include its own context. In block 607, theSource TRP and the Target TRP perform Inter-TRP coordination. Thiscoordination may be to determine which TRP will share which resourceswith the WTRU. In block 608, the WTRU successfully receives thetransmission and updates the configuration of the serving TRP withinformation that may be related to the new resources granted to the WTRUby the Target TRP.

To enable a WTRU or the network to determine that a WTRU would beoptimally served by a specific TRP or set of TRPs, the WTRU may need tomake measurements, and may need to make those measurements repeatedly,as the optimal TRP may change based on changes in conditions includingmobility. Such measurements may include at least one of the measurementtypes discussed below.

For example, a WTRU may measure received power on a set of resources.The set of resources may be semi-static, or may be dynamicallyindicated. Each serving TRP may have independent sets of resources onwhich a WTRU may measure received power. A set of TRPs, e.g. a TRP group(TRPG), may also share at some resources on which a WTRU may make ormaintain measurements.

A WTRU may measure the total received power over one or more symbols,covering a pre-determined or configurable bandwidth. A WTRU maydetermine the quality of a signal from a serving cell. One method todetermine received quality may be to divide the received power by thesignal strength.

A WTRU may also make measurements, possibly on a set of configurableresources, to determine a level of interference it experiences whenserved by a specific TRP on a specific set of resources. A WTRU maymeasure one type of interference or may measure more than one type. AWTRU may measure interference on a signal from a TRP, interference on asignal from any TRP within a TRPG, and/or interference on a signal fromall TRPs within a TRPG.

A WTRU may determine the Signal to Interference plus Noise Ratio (SINR)when served by at least one TRP. A WTRU may also make measurements todetermine channel occupancy. For example, a WTRU may have an ability toaccess an unlicensed channel.

TRP Load may be measured. The TRP load may be measured using a DLchannel usage, an UL channel usage, or both.

To make measurements on one or more serving TRPs, a WTRU may firstdetermine a resource on which it may make the measurement. For example,a WTRU may autonomously find a signal transmitted by the TRP thatenables the WTRU to make measurements fulfilling appropriaterequirements. A WTRU may also be notified of the resources on which tomake measurements. This notification may occur dynamically.

A WTRU may determine the presence of a signature sequence autonomouslyand/or based on pre-determined rules. For example, a WTRU may blindlydetect a first instance of a signature sequence and may determine thepresence of further signature sequences for the TRP based on apre-determined function. The pre-determined function may be fixedseparation in time and/or frequency from the first detected signaturesequence, but other pre-determined functions may be used additionally orinstead of those recited. A WTRU may also be notified, possibly by theTRP, of the presence of a signature sequence, or a function to determinethe presence of a signature sequence.

A mobility measurement may be performed by the WTRU on the signaturesequence itself. For example, the WTRU may determine a received power ofthe signature sequence, and/or any interference present when decodingthe sequence.

A WTRU may also perform measurements on a reference signal present formeasurements. A signature sequence may point the WTRU to resources whereit may expect a reference signal (RS) to be present for measurementpurposes, which may occur implicitly or explicitly.

A WTRU may use a function to determine resources on which the RS istransmitted. This would be one example of implicitly pointing the WTRUto resources where it may expect a RS. The function may use a parameterof the signature sequence to determine a parameter of the RS. Theparameter of the signature sequence that may indicate the resources usedfor RS may include at least one of: resource mapping; timing of thesequence; the sequence used; and/or antenna ports.

Resources used for transmission of the signature sequence (e.g. thecombination of symbols and subcarriers) may indicate the relevantparameters of the RS.

Timing of the sequence may indicate a set of parameters of the RS, whichmay include timing of the RS. A WTRU may expect the RS to be in specificsymbols or subframes, and it may determine the symbol or subframenumbering based on the timing of the signature sequence. The WTRU mayalso expect a specific timing offset between the signature sequence andthe transmission of the RS.

A signature sequence may be transmitted using one of many possiblesequences. The sequence of the signature sequence may map to specificparameters for the RS.

Antenna ports used to transmit the signature sequence may indicate a setof parameters of the RS. For example, a beam may be used to transmit asignature sequence and the same beam may be used to transmit the RS.These are examples of implicit indication. Other manners of implicitindication may be used.

A signature sequence may encode parameters of the RS. This is oneexample of an explicit indication of the RS by the signature sequence.For example, the signature sequence may be detected and demodulated bythe WTRU and the information may indicate some parameters of theassociated RS. The signature sequence may also map to an entry in anaccess table. The entry may indicate some parameters of the associatedRS. These are examples of explicit indication. Other manners of explicitindication may be used.

A WTRU may also perform mobility measurements by using a UE-dedicatedRS. The UE-dedicated RS may be configured by the one or more servingTRP. The UE-dedicated RS may also be transmitted, which may occurperiodically or aperiodically. Aperiodic transmission may be indicatedby one or more serving TRPs. For example, aperiodic transmission of RSmay be multicast to an appropriate group of WTRUs sharing similar RSconfiguration.

Furthermore, the UE-dedicated RS may also be transmitted only inside oroutside a transmission burst. A transmission burst may be defined as aperiod of time for which a serving TRP has DL transmission to, orexpects an UL transmission from, any of its WTRUs. For the sake ofUE-dedicated RS transmission, a transmission burst may also be a periodof time for which a serving TRP has DL transmission to or expects an ULtransmission from the WTRU itself.

The UE-dedicated RS may be transmitted upon request from the WTRU. Themethod by which a WTRU may request the transmission of UE-dedicated RSmay be indicated in the access table, or may be configured by one ormore serving TRP.

The UE-dedicated RS may be transmitted as a result of transmission of achannel or the contents of another transmission. For example, a WTRU mayfeedback certain measurements performed on a first RS. Depending on thevalue fed back, the WTRU may expect the transmission of a second RS onwhich it may perform mobility measurements. A WTRU may also report NACKfor a DL transmission. The WTRU may also expect the transmission of anRS to perform mobility measurements. This may be based on a redundancyversion of the transmission that caused the NACK.

The WTRU may also be configured to perform periodic mobilitymeasurements. The WTRU may also be configured to perform mobilitymeasurements when appropriate RS is present. This may be for eitheron-demand RS transmission or TRP selected RS transmission.

A WTRU may be required or expected to make measurements whenever it hasUL data to transmit to at least one TRP, or whenever it expects DLtransmissions from at least one TRP. For example, a self-containedsubframe may be used, composed of a control region, a DL transmissionregion, an UL transmission region and appropriate guard periods. If theWTRU is scheduled for either DL transmission or UL transmission, orboth, during such a subframe, the WTRU may perform mobilitymeasurements, possibly on an RS in the same subframe.

A WTRU may be triggered to perform a mobility measurement on a servingTRP by at least another TRP. A measurement being triggered on anotherserving TRP sharing the same signature sequence may cause such atrigger. A measurement being triggered on at least one other serving TRPusing a different signature sequence may also trigger a mobilitymeasurement event at the WTRU. Detection of another TRP, sharing or notsharing the same signature sequence, may also cause a mobilitymeasurement. Increased interference from another TRP sharing (or notsharing) the same signature sequence, may also trigger a mobilitymeasurement.

A WTRU may be triggered to perform a mobility measurement based on WTRUlocation, speed or heading. For example, a WTRU may also be triggered toperform a mobility measurement on a serving TRP based on the WTRUslocation, speed, heading. A WTRU may transition from a non-moving stateto a moving state, which may trigger a mobility measurement. The WTRUmay also move from one predetermined area to a different pre-determinedarea, which may also trigger a mobility measurement. Predetermined areasmay be determined by the WTRU, or may be signaled by the network, andmay be defined by exact geographic coordinates (latitude, longitude, orthe such) or may be relative to specific reference physical locations ordistance from such locations, of which the WTRU is also aware. The WTRU,in such cases, may determine its own location, speed, heading, etc.independently using location technology such as GPS, or by using networkbased methods and having the location signaled to it by the network.

A WTRU may be configured with a list of areas from which it maydetermine if mobility measurements are required. A WTRU may alsoautonomously determine such a list of areas. The list may includegeographic locations. Lists may also include sets of TRPs, and mayinclude configurations to enable mobility measurements of the TRPs. Thesets of TRPs per geographic list may be maintained by the WTRU. Forexample, a WTRU may add a TRP to a list upon making a relevantmeasurement. A WTRU may also remove a TRP from a list upon expiration ofa timer. The timer may be started at the moment of a most recentmobility measurement on a TRP.

A WTRU may also determine a trigger for a mobility measurement based onits distance from a specific TRP. A WTRU may receive the geographicallocation of one or more TRPs. The WTRU may receive this information frombroadcast or dedicated signaling from the TRP or through informationfrom the access table. If there is a change in distance, or if adistance meets a specific triggering criteria, a mobility measurementmay be triggered. For example, the WTRU may trigger a mobilitymeasurement if the distance between the WTRU location and the signaledTRP location exceeds a threshold.

A WTRU may report a measurement whenever it has completed one. The WTRUmay also have periodic resources on which it may report mobilitymeasurements. Such resources may be similar to CSI feedback resources.The WTRU may be triggered to report measurements aperiodically by aserving TRP. Such a trigger may include an UL grant of resources, onwhich the WTRU may report one or more measurements.

A WTRU may be triggered to report measurements. When a measurement istriggered, the WTRU may feedback such measurement. Whenever ameasurement has been, or may be, performed upon detection of a newsignature, the WTRU may be triggered to report measurements. The WTRUmay also be triggered to report measurements when a measurement hasbeen, or may be, performed upon detection of a new RS for the samesignature.

The WTRU may also be triggered to report measurements based onthresholds, which may be absolute or relative to other measurements. Thecomparison between a measurement and a threshold may depend on whetherthe measurements are for TRPs sharing signature sequences. A WTRU mayalso be triggered to report measurements when the WTRU is provided withresources to report measurements, or based on a change of location,speed, heading, or distance from one or more TRP, as determined by theWTRU.

Measurements may be reported via different mechanisms. For example,measurements may be reported on physical channels used for ULtransmissions. Mobility measurements may be included in periodicfeedback or aperiodic feedback. Mobility measurements may also beincluded in UCI transmitted within an UL grant for data transmission. AWTRU may also report mobility measurements on physical layer resources.A WTRU may also report mobility measurements on a MAC CE.

A WTRU may reuse CSI feedback resources. In reusing CSI feedbackresources, the WTRU may include an identifier to indicate the CSIfeedback report has been supplanted by a mobility measurement report.The identifier may also indicate that mobility measurements have beenconcatenated or put into the CSI feedback report.

The WTRU may report mobility measurements in HARQ feedback. The presenceof mobility measurements may depend on the feedback itself. For example,an ACK may indicate to the serving TRP that no mobility measurements areincluded, which may occur because a channel is good enough to supportthe transmission. A NACK, possibly on a specific retransmission, mayalso indicate to the serving TRP that a mobility measurement is alsoincluded.

A WTRU may report mobility measurements in the UL portion of aself-contained subframe. For example, a WTRU configured with RS formobility measurements, or configured to make mobility measurements on aself-contained subframe, may transmit the mobility measurement in the ULportion of the subframe. When a measurement triggers a mobilitymeasurement or a mobility measurement report in a self-containedsubframe, the report may also be transmitted in the UL portion of thatsame subframe.

A WTRU may maintain measurements of neighbor TRPs for later use. A TRPmay be identified by a WTRU by a transmitted signal, a signaturesequence, or assistance from another TRP.

For example, a reference signal transmitted by the TRP may also be usedby the WTRU to synchronize to the TRP. The transmitted signal may alsobe transmitted by a TRP other than the TRP to be identified. Thetransmitted signal may also be transmitted by another WTRU, possibly oneserved by the TRP. The transmitted signal may be periodic, or may beon-demand by the WTRU.

A signal may be transmitted periodically with at least some parametersidentifying at least one TRP. The signature sequence may map to an entryin an access table transmitted less often. The access table may providesome TRP system information.

For example, a first TRP may be identified by assistance informationtransmitted from a second TRP. Although a WTRU has identified thepresence of a TRP, it does not necessarily follow that a WTRU hasperformed any measurements.

A WTRU may detect and synchronize to a TRP that is not currently servingthe WTRU, which may be referred to as a neighboring TRP. Upon detectinga neighboring TRP, the WTRU may classify the TRP based on whether itshares a signature sequence with at least one serving TRP. If asignature sequence is shared, the access table may provide a list of RSson which to synchronize to different TRPs within the TRPG sharingsignature sequence. The WTRU may also assume some synchronization isshared between TRPs that share a signature sequence. For example, theWTRU may use synchronization to a serving cell as coarse synchronizationto a neighboring cell sharing signature sequence. The access table mayalso provide the resources where RS are located to perform measurements.

If the signature sequence of a neighboring TRP is not shared by at leastone serving TRP, the WTRU may not assume any shared synchronization witha serving TRP. In such a case, the WTRU may require multipletransmissions of the signature sequence before assuming adequatesynchronization to perform mobility measurements.

The search for neighbor TRPs with signature sequences not shared by atleast one serving TRP, may be configurable and may be assisted by aserving TRP. For example, a WTRU may receive a signature sequenceidentity or a set of resources where it may look for a new signaturesequence, from at least one of its serving TRPs. A WTRU may also beinstructed by at least one of its TRPs to search for other signaturesequences without further assistance. A WTRU may also autonomouslysearch and detect neighboring TRPs using other signature sequences.

Neighbor TRP measurements may use any of the methods and measurementtypes proposed herein for serving TRP measurements.

If a signature sequence is used by at least one serving TRP, the WTRUmay be expected to perform measurements on all TRPs using the signaturesequence. If a signature sequence is not used by at least one servingTRP, the WTRU may be configured to measure a neighbor TRP upon detectionof the signature sequence or TRP. In this case, the WTRU may be expectedto measure one, some, or all TRPs sharing the newly discovered signaturesequence.

If a measurement on at least one serving TRPs achieves a threshold, aWTRU may be triggered to perform a measurement on a neighbor TRP. Forexample, received power on at least one serving TRP may fall below, orgo above, a threshold. Received power is just one example of ameasurement that may be use to trigger a measurement.

If a WTRU is unable to properly decode a number of transport blocksusing less than a number of retransmissions, this kind of change indemodulation performance by the WTRU may trigger a measurement. Thenumber of transport blocks, and/or the amount of retransmissions, may beconfigurable.

A measurement triggered on a serving TRP may trigger a measurement on aone or more neighbor TRPs. This may be applicable if the neighbor TRPsshare a signature sequence with the serving TRP for whom a measurementhas been triggered.

A change in the WTRUs location, speed, heading, or distance between theWTRU and the neighbor TRP may also trigger a measurement. This may alsobe combined with a requirement that the TRP shares the same signaturesequence.

A WTRU may determine measurement resources from an access table. If thesignature sequence of a neighboring TRP is the same as at least oneserving TRP, the WTRU may receive assistance from the serving TRP. TheWTRU may also obtain resources from at least one serving TRP, and it mayuse those resources to demand measuring resources from the neighboringTRP. For example, the WTRU may be provided resources by a serving TRPfor an UL transmission to a non-serving, TRP. The UL transmission may beto trigger the neighboring TRP to transmit possibly UE-dedicated RSs formeasurements.

If the neighboring cell does not share a signature sequence with atleast one serving TRP, the WTRU may be required to trigger RSs formeasurements by using shared UL resources. For example, the WTRU maytransmit a probing signal. Such a probing signal may be transmitted onresources specific to a signature sequence. The probing signal may alsoindicate the signature sequence for which it is being transmitted. Theprobing signal may also trigger the transmission of the required RSs, orit may trigger the transmission of, possibly UE-dedicated, systeminformation. System information may be included in a triggered accesstable transmission.

Neighbor TRP measurements may be reported in a similar manner to themethods defined herein for reporting measurements from serving TRPs.Neighbor TRP measurements may also be reported whenever a serving TRPmeasurement is reported. A subset of neighbor TRP measurements may alsobe reported. For example, the WTRU may rank the neighbor TRPs based ontheir measurements and only report the best. The WTRU may reportmeasurements for all TRPs sharing the same signature sequence as thebest TRP. The WTRU may report a measurement for a single TRP persignature sequence. The WTRU may report the measurements for a set ofthe best TRPs, independent of whether they share signature sequence ornot.

A neighbor TRP measurement report may be sent to different destinations.A WTRU may report a neighbor TRP measurement to at least one of itsserving TRPs. For example, the WTRU may report neighbor TRP measurementsto any serving TRP sharing the signature sequence of the neighbor. TheWTRU may also report neighbor TRP measurements to a primary serving TRP,regardless of whether the neighbor TRP and primary serving TRP share asignature sequence.

The WTRU may also report measurements to the TRP for whom themeasurement applies. This may enable WTRU-autonomous handover.

A WTRU may also report measurements to any TRP that is capable ofhearing the WTRU. For example, a WTRU may be configured with resourceson which it may report measurement feedback. Such resources may beshared among TRPs, such as among TRPs sharing a signature sequence. TheWTRU may also be provided shared resources on which to reportmeasurements. The shared measurement resources may be shared per TRPG,for example, sharing same signature sequence.

Beyond simply reporting back a measurement, a WTRU may be triggered toperform other, actions upon obtaining a measurement. Actions to beperformed may be configurable. A WTRU may be triggered to perform randomaccess to that neighbor TRP based on a measurement of at least oneneighbor TRP, satisfying at least one criterion such as a measurementthreshold. Such an RA may be modified to include a cause value to theneighbor TRP. The cause value may indicate the measurement or the valueof the measurement that triggered the RA. The cause value may alsoindicate at least one source TRP. For example, a criterion for such anaction may be if a neighbor TRP measurement is offset greater than themeasurement of at least one serving TRP. In such a case, the RA causevalue may indicate the serving TRP whose measurements are offset lowerthan that of the neighbor TRP. Such a measurement-triggered RA may onlybe possible if the neighbor TRP shares a signature sequence with atleast one serving TRP. A measurement-triggered RA may include some WTRUinformation to enable appropriate handover between at least one sourceTRP and the target TRP.

A WTRU may build and maintain a list of neighbor TRPs, which it mayprovide to the network. Such a list may comprise the neighbor TRPs thatare currently being measured by the WTRU. It may also comprise the listof TRPs for which the TRP measurements have met some specific criteria.Such criteria may be based on any of the measurements described herein.The list may also comprise the neighbor TRPs which the WTRU is able todetect. The list may also comprise the TRPs that belong to one or a setof specific system signatures. The neighbor TRP list may also comprisethe list of TRPs for which the conditions for the WTRU to perform aWTRU-autonomous handover are satisfied.

A WTRU may transmit the neighbor TRP list to one or more of its servingTRPs. One reason for sending the neighbor TRP list may be to allow a TRPor the network to determine, in the case that a WTRU context needs to betransferred directly from one TRP to another, which TRPs needs to beinvolved in this context transfer. Another motivation may be to allowthe network to choose TRPs to which a WTRU's DL traffic from the networkneeds to be sent, and to choose which TRPs need to coordinate resources.A WTRU's data may be provided to multiple TRPs for DL transmission. Theactual TRP or TRPs transmitting the data may be triggered by the WTRU,which may involve the use of an autonomous handover operation.

As a WTRU moves, it may update and report a new version of the neighborlist to the network. Updates may include adding or removing neighborTRPs from the list, and updates to the list may be triggered by certainfactors or circumstances. A WTRU may update based on one or moretriggers. If measurements associated with a TRP meets or fails to meetone or more specific criteria, that may trigger adding or removing aneighbor TRP from the list. A neighbor TRP may also be added to orremoved from the list if a distance between the WTRU and a specific TRPis above/below a specific threshold, or if speed of a WTRUincreases/decreases beyond a specific value. For example, the WTRU maybe configured with a specific minimum number of TRPs in the measurementlist when its speed is above a certain amount, or a WTRU may beconfigured with a desired measurement list size corresponding to eachspeed range. A neighbor TRP may also be added to or removed from thelist if a new signature sequence is detected. In this case one or moreTRPs associated to the new signature sequence may be added). A neighborTRP may also be added to or removed from the list if a TRP from a TRPGis added to the neighbor list, in which case all other TRPs in the TRPGmay also be added.

The WTRU may send the neighbor list to the network as triggered by anumber of situations. The WTRU may be configured to periodicallytransmit the neighbor list. The WTRU may also be triggered by at leastone TRP, perhaps a serving TRP, to transmit the neighbor list. The WTRUmay also transmit the neighbor list upon a change to the list, such asaddition or removal of a neighbor on the list. The WTRU may alsotransmit the neighbor list upon a random access or WTRU-autonomoushandover, as described below.

An architecture diagram for Random Access (RA) is shown in FIG. 7. AWTRU 700 may begin by transmitting an RA preamble via random accesstransmissions 701, which may be detectable by multiple TRPs 710, up toand including all TRPs 710, in TRPG 320. The WTRU 700 may then receive aRAR 702 from one TRP 710 and another RAR 702 from a second TRP 710, inresponse to random access transmissions 701. The WTRU 700 may begin datatransmission 703 with the first TRP 710 based on the RAR informationreceived from the first TRP 710, and may also store the RAR 702 from thesecond TRP 710. When the WTRU changes location in a mobility direction,or when the first TRP becomes non-responsive or the communicationbecomes slow below a threshold, the WTRU 700 may cease transmittingbetween itself and the first TRP 710 and may, without another initialexchange of RA information, begin transmitting to the second TRP 710instead, based on the new location of the WTRU and its relativeproximity to the first TRP 710 and the second TRP 710. This may occurwithin a single cell of operation. The ability to seamlessly switchbetween TRPs because of stored RAR data allows greater mobility andreduces mobility related signaling and a number of always-on signals.

A WTRU may be triggered to perform RA to a neighboring TRP by ameasurement or combination of measurements. For example, a WTRU maydetermine that a neighboring TRP may have become stronger (e.g. havehigher received power) than a serving TRP. A measurement on a neighborTRP may also indicate to the WTRU that the neighboring TRP may be addedto the set of serving TRPs. This may depend on whether the neighbor TRPa shares signature sequence with at least one serving TRP.

A WTRU may perform RA to a neighbor TRP if the WTRU has determined thatit has suffered a decrease in transmission performance from at least oneserving TRP. Such a decrease in performance may be determined from aninability to decode one or more transport blocks (TB). For example, uponhaving at least a threshold number, x, TB undelivered with an allowednumber of retransmissions, for example, by requiring RLCretransmissions, a WTRU may determine that it has suffered performancedegradation. The x TB may be x consecutive TB, or, the x TB may be any xTB within a time period or total number of transmitted TBs. The timeperiod or the total number of transmitted TBs may be configurable.

A WTRU may be indicated to perform RA on a neighboring TRP by at leastone serving TRP. The indication may be WTRU-specific, group-specific orTRP-specific. The indication may be on a physical channel or may bebroadcast. The indication may also be added to an access table entry.For example, a WTRU served by a TRP should continue monitoring theaccess table entry to which it is mapped by the serving TRP's signaturesequence. The indication may be by a change of one or more parameters ofthe signature sequence.

A WTRU may determine that its current set of serving TRPs may notsatisfy its UL or DL transmission needs. In an example, a WTRU may haveURLLC transmissions that require macro diversity. In order to achievethe required macro diversity, the WTRU may need to increase its servingTRP set. As such a WTRU may perform RA to at least one neighboring TRP.

For example, a WTRU may determine that it has a change in transmissionrequirements. This may be manifested as a change in desired SOM. TheWTRU may therefore perform RA to a neighboring TRP that can support therequired SOM.

For example, a WTRU may determine that based on its speed it would bebetter served by a TRP with a larger or smaller coverage area. The WTRUmay then perform RA to at least one appropriate TRP.

For example, a WTRU may have a list of possible TRPs per geographicalarea. Upon entering a geographic area, as determined by a locationfunction, the WTRU may attempt RA on at least one TRP.

For example, a WTRU may have RLF to at least one serving TRP. In such acase, the WTRU may perform RA to at least one neighboring TRP, or to theserving TRP from which it suffered RLF.

The RA procedure may depend on whether the RA is to a TRP that sharessignature sequence with at least one serving TRP or not. For example,for RA to perform handover to a target TRP sharing signature sequencewith at least one source TRP, the WTRU may assume configured ULresources are still valid. The WTRU may immediately continuepre-scheduled UL transmissions upon reception of a RAR. The WTRU mayalso assume that configured DL transmissions (e.g. of reference signals,or semi-persistent scheduled transmissions) are also still valid.

On the other hand, for a RA to a TRP that does not share a signaturesequence with at least one serving TRP, the WTRU may need to provide theTRP with more information before expecting new scheduling grants. Thismay include HARQ processing state, WTRU contexts, security information,etc. Such information may be shared upon reception of a grant from a RARmessage. Such information may also be shared in an enhanced preambletransmission. Furthermore, any configured UL resources may be assumed nolonger valid.

An RA preamble transmitted by a WTRU may be targeted for a specifictarget TRP, or any TRP within a TRPG, which may be comprised of TRPssharing same signature sequence. Such an RA may use resources indicatedby at least one source TRP. For example, the resources may be determinedto be the same as those used for a source TRP, if the source TRP sharessignature sequence with the target TRP.

The RA preamble may be transmitted without an intended target. This maybe applicable to any TRP within a group of TRPs sharing a signaturesequence or to any TRP even not sharing a signature sequence. Such an RAmay be considered a probing type mechanism to enable any TRP capable ofdetecting the RA preamble to being transmitting at least one signal. Forexample, the RA preamble may enable all neighboring TRPs to transmittheir signature sequence, or system information, or to transmit an RS toenable measurements.

A WTRU may receive a single random access response (RAR). For example, aset of TRPs may coordinate to transmit a single RAR. The RAR may includeinformation on the set of TRPs. From the RAR, the WTRU may be able todetermine one or more TRPs to connect to.

In another solution, a WTRU may receive multiple RARs, possibly one perTRP that successfully received the RA preamble—or possibly one RAR perTRPG. Optionally, a WTRU may receive one RAR per set of TRPs sharing asignature sequence.

Upon reception of multiple TRPs, the WTRU may select one or more basedon measurements, a signature sequence of the TRP transmitting the RAR,WTRU context sharing, timing of reception of RAR, TRP capabilities;and/or a parameter indicated in the RAR.

A WTRU may select on or more based possibly on measurements made on RSprior to the transmission of RA preamble. Measurements may also be madeon signals transmitted with the RAR.

A WTRU may give priority to TRPs sharing a signature sequence with atleast one source or serving TRP. A WTRU may also give priority to a TRPnot sharing a signature sequence with at least one source or servingTRP. This may enable the WTRU to be served by a new set of TRPs,possibly enabling more seamless mobility.

A WTRU may give priority to a TRP sharing WTRU context, or HARQprocessing or scheduler with at least one source or serving TRP. A WTRUmay also prioritize a TRP that transmitted its RAR earlier than anotherTRP. The WTRU may also interpret the timing of a RAR as a function ofthe latency achievable in transmissions to or from the TRP.

A RAR may include TRP capabilities, and a WTRU may prioritize TRPs whosecapabilities better match the WTRU's requirements. TRP capabilities mayalso be known by the WTRU a priori to the transmission of the RAR,because, for example, the TRP capabilities may be included in an accesstable.

The WTRU may also select a RAR based on a parameter transmitted in theRAR. The parameter may include current TRP load, traffic, transmissionlimitations, UL and DL configuration, or other parameters. Transmissionlimitations may be used to reduce interferences between TRPs.

A WTRU may select more than one RAR representing more than one TRP. Thismay enable the WTRU to be configured for carrier aggregation, or dualconnectivity or CoMP. The selection of the more than one RAR may dependon similar criteria as defined for the selection of a single RAR. In anexample, the WTRU may select one RAR per group of TRPs; where a group ofTRPs may define a set of TRPs sharing same signature sequence. The WTRUmay also select all RARs from a TRPG (that is to say all RARs comingfrom TRPs sharing a signature sequence). The TRPG from which a WTRU mayselect all RARs may be determined as being one whose signature sequenceis, or is not, shared with at least one source or serving TRPs.

A WTRU may select a subset of RARs to continue the full RA process with.However, the WTRU may also store the set TRPs (as well as anyinformation included within the RARs) that transmitted unused RARs forpossible future rapid random access. For the set of stored TRPs, theWTRU may transmit an acknowledgement of received RAR, but discontinuedRA process. Furthermore, the WTRU may maintain measurements on suchTRPs.

A RAR may include at least one of: a timing advance; a set of ULresources; system information; an indication of seamless mobility;and/or an indication of a need for WTRU information. Resources for an ULtransmission, or resources for scheduling request may be included in aRAR.

System information may be transmitted on-demand and/or on WTRU-dedicatedresources. The RAR may include system information. The RAR may alsoinclude resources on which a WTRU may demand system information, whichmay include updated system information.

In the case of an indication of seamless mobility, a WTRU may assumethat upon reception of a RAR, all of its context and configurations froma source TRP are maintained. For example, a target TRP may not be ableto obtain WTRU contexts, HARQ processing state, scheduling information,or WTRU configurations from at least one source or serving TRP. Thetarget TRP may also not share a signature with at least one source TRPand such WTRU information may only be shared dynamically by TRPs sharingsignature sequence. The RAR may indicate to the WTRU that it needs suchinformation to be able to perform PHY layer mobility. The RAR mayprovide the WTRU with UL resources to transmit such information.

The RAR may also provide a set of UL resources to continue transmittinga grant provided by a source TRP. The RAR may also provide a translationfunction, and/or translation rules, to allow the WTRU to translatebetween resources granted by a source TRP to the corresponding resourcesthat should be used in the target TRP in case the transmission occurs inthe target.

The location of certain channels and signals from the source TRP to thetarget TRP may be indicated. These signals may include PUCCH, SR, orSRS, A translation function and/or translation rules, to allow the WTRUto translate the location or nature (time, frequency, scrambling code)of the channels or signals, may also be indicated.

An indication about whether a resource granted in the source TRP is alsoavailable in the target TRP may also be provided.

A WTRU may obtain required information from at least one source orserving TRP and perform a transmission to a target TRP. The WTRU mayalso indicate to at least one source or serving TRP to provide therequired information, or a subset thereof, to the target TRP. Such anindication may include a target TRP identifier. Such an indication mayalso provide radio resources on which the one or more source or servingTRPs may transmit the required WTRU information.

A RAR may also indicate to the WTRU an inability to perform PHY layermobility, and may also indicate that it has begun higher-layer mobilityprocedures to obtain the appropriate WTRU information.

If a WTRU does not receive a RAR from a target TRP, it may indicate to aserving TRP, e.g. a source TRP, that it has attempted RA to a neighborTRP and failed to receive a RAR. Such an indication may include a targetTRP identifier, which may be a signature sequence. Such an indicationmay also provide a reason why the WTRU is attempting the RA to thetarget TRP. The reason may include a desire to perform handover, adesire to add a serving TRP to an existing set, a desire to connect to atarget TRP for one-shot transmission, or a desire to receive systeminformation from target TRP. Other reasons may also be included.

In the case of a desire to perform handover, a WTRU may also indicatethe set of TRPs that it wished to drop upon completing the handover tothe target TRP(s).

A serving TRP may be added to an existing set, which may be used forcarrier aggregation, dual connectivity or CoMP.

A WTRU may request connect to a target TRP for a one-shot transmission,which may be used when, the WTRU wishes to connect to a target TRP toindicate its presence, or that it suffers detrimental interference fromthe target TRP.

Failing to receive a RAR from a target TRP may also be a trigger for aWTRU to report mobility measurements to at least one serving TRP. RadioLink Failure (RLF) may be determined and declared by the WTRU for one,some or all serving TRPs. For example, RLF may be determined on anindividual TRP basis, regardless of whether its signature sequence isshared. RLF may also be determined and declared on a TRPG if one, someor all serving TRPs within that TRPG suffer RLF.

A WTRU may experience RLF if it fails to find an adequate target TRP andat least one measurement on at least one serving TRP is lower than athreshold. For example, a WTRU with a single serving TRP may find thatreceived power has decreased below a threshold, possibly for a certainperiod of time, for a set of consecutive measurements, or for a setnumber of measurements within a time period. Decreased power may triggerthe WTRU to attempt to find a target TRP. If the WTRU does not find anacceptable TRP within a set period of time, it may declare RLF. Thedeclaration of RLF may depend on whether the WTRU is capable of findinga target TRP using the same signature sequence as at least one servingTRP, or a target TRP using a different signature sequence as all servingTRPs. For example, a WTRU may have the ability to declare RLF on a TRPGbasis, where the TRPs in the TRPG share the same signature sequence. Inthis example, a WTRU may find a target TRP that does not share signaturesequence with any serving TRP, and may even perform RA to that targetTRP. However, the WTRU may declare RLF on any TRPG for which it did notfind a new adequate target TRP.

A WTRU may also declare RLF if at least one measurement on at least oneserving TRPs is lower than a threshold and it fails to receive a RARafter attempting RA on at least one target TRP.

A WTRU may also declare RLF if at least one measurement on at least oneserving TRP is lower than a threshold, and it fails to complete RA (e.g.fails to receive RAR) to that at least one serving TRP. A WTRU may alsodeclare RLF on a serving TRP if it is incapable of decoding a transportblock on a final HARQ retransmission. In another solution, a WTRU maydeclare RLF on a serving TRP if it has reached maximum RLC transmissionsfor a transport block. A WTRU may also declare RLF if it has exceededperformance criteria of a radio bearer and/or SOM. For example, a WTRUmay declare RLF if it is incapable of achieving a certain required delayfor a SOM. In this example, the cause of RLF may be indicated upondeclaration of RLF. This may enable the network to determine that a TRPor TRPG are still able to provide certain connectivity to a WTRU, justnot the one required for that SOM.

A WTRU may also declare RLF if a measurement shows that it may not beable to achieve the required average performance. For example, a firstmeasurement, which may be a received power measurement, may indicatethat a WTRU is capable of achieving certain instantaneous performance.However, a second measurement, which may be a number of diversitybranches, may indicate that on average the WTRU will not achieve therequired performance.

A WTRU may also declare RLF if it is incapable of being configured with,or detecting, required reference signals. For example, a WTRU may beindicated WTRU-specific and possibly dynamic reference signals. Uponexpiration of a first set of reference signals, if the WTRU is notconfigured with a new set, or is incapable of detecting the new set, itmay declare RLF.

RLF may be determined and declared per direction of transmission. Forexample, a WTRU may determine that it is no longer capable of achievinga required level of performance for UL transmissions to a serving TRP.However, the same WTRU may be capable of DL transmissions from the sameset of TRPs. Or, the reverse may be true. In this case, a WTRU maydeclare RLF with an indication of the type of transmissions for which itis declaring RLF, either UL or DL.

In another solution, a WTRU may transmit an UL signal, enablingmeasurements done by at least one serving TRP. The UL signal may beperiodically transmitted by the WTRU. The UL signal may also betransmitted upon being triggered by the WTRU. A trigger may include anyof the aforementioned causes for detection of a neighbor TRP, RA to aneighbor TRP, or declaration of RLF. The UL signal's transmissionparameters may be semi-static (e.g. indicated in an access table or insystem information) or may be configured and WTRU-specific. Upontransmission of an UL signal, the WTRU may start a timer. Uponexpiration of the timer, if the WTRU does not receive a response fromthe TRP to which the signal was targeted, the WTRU may declare RLF tothe serving TRP.

RLF declaration may depend on the type (e.g. SOM, or URLCC/eMBB/massiveMTC) of transmissions for which the serving TRP was used. For example,different thresholds may exist for different types or modes oftransmission. Furthermore, an RLF may be applicable only to one type ormode of transmission. In this example, a WTRU may declare RLF to a TRPfor URLLC but may still be capable of eMBB.

A WTRU may be configured with two different thresholds, where the firstthreshold is higher than the second threshold. The first threshold maybe a pre-RLF threshold and the second threshold may be a RLF threshold.WTRU may perform a first set of actions if the measurements of systemsignature and/or reference signal goes below first threshold and asecond set of actions when the measurements of system signature and/orreference signal goes below the second threshold. For example, when oneor more serving TRPs goes below first threshold, WTRU may perform one ormore of the actions described below.

A WTRU may transmit the request for measurement reference signalstowards non-serving TRPs within a TRPG. For example, such measurementreference signals may be WTRU specific or TRP specific reference signalsthat are turned off for power saving. A WTRU may also transmit ULmeasurement signals on preconfigured WTRU-specific resources. One ormore TRPs may listen on those UL resources and measure WTRU'stransmissions.

The WTRU may also be configured to receive downlink control informationaccording to different transmission methods. Different transmissionmethods for downlink control information may imply different levels ofreliability. Different levels of reliability may be realized by the WTRUbeing configured with more than one control channel, control channelsearch spaces, aggregation levels for decoding of the DCI, sets ofcontrol channel elements, or the likes. For example, the WTRU maymonitor only a first control channel. The WTRU may also monitor acontrol channel search space when the serving TRP is above the firstthreshold. When the serving TRP is below the first threshold, WTRU maystart monitoring a second set of control channels or control channelsearch space. The first set of control channels may be TRP specific anda second set of control channels may be common to more than one TRP orall TRPs within the serving TRPG. A non-serving TRP may also transmit ahandover command on the second set of control channel (or) controlchannel search space based on a WTRU measurement report or ULmeasurement signals.

A WTRU may also trigger initial access procedures (e.g. random access)towards non-serving TRPs within the TRPG. A WTRU may include additionalinformation regarding the serving TRP ID, radio bearer configuration,WTRU context, reason for failure etc to those TRPs. In another option, aWTRU may perform RA-less autonomous HO procedure described below.

When one or more serving TRPs goes below the second threshold, a WTRUmay declare RLF and perform the above mentioned actions towards TRPs inother TRPGs, TRPs in other layers, or LTE-Evo eNB.

If a WTRU is served by multiple TRPs, the WTRU may send a declaration ofRLF to one of its other serving TRPs. For example, the WTRU may send adeclaration of RLF to any other serving TRP sharing a signature sequencewith the TRP for which it experiences RLF.

If a WTRU is served by a single TRP (or a single TRP for a signaturesequence), the WTRU may begin re-establishment procedures. If a WTRU isserved by a single TRP, or a single TRP for a signature sequence, theWTRU may also begin to search for another TRP sharing the signaturesequence. If an adequate target TRP is discovered, the WTRU may beginRA, possibly indicating as cause, “RLF to another TRP sharing signaturesequence.” A WTRU may also attempt RA to any other adequate TRP, whetherit shares signature sequence with the TRP experiencing RLF or not.

A WTRU may also attempt quick RA to a TRP for which it had stored apreviously transmitted successful RAR, but for which it had notcontinued with the RA procedure. In such a case, the WTRU may indicateto such a target TRP that it saved parameters transmitted in a previousRAR and that it wishes to continue with this interrupted RA procedure.To enable this, it is possible that the RAR includes UL resources onwhich a WTRU may continue with such interrupted RA procedure. There mayalso be an associated timer indicating the time for which such resourcesare valid.

WTRU behavior upon experiencing RLF may depend on what the use case forthe connection. For example, a type or mode of transmission (e.g. SOM,or URLLC/eMBB/massive MTC) may dictate to the WTRU the behavior it maytake upon declaration of RLF. Accordingly, a WTRU may experience RLF forone mode (e.g. URLLC), but may be able to indicate to the TRP, possiblyusing another mode, that it experienced RLF for the first mode.

A WTRU may perform RA-less mobility, which may also be referred to asWTRU-autonomous HO. Triggers to perform such mobility may be similar toaforementioned triggers for detection of neighbor cells, triggers formeasurements, triggers for measurement reporting or triggers forRA-based mobility. Furthermore, a declaration of RLF may initiateRA-less mobility.

The ability to perform RA-less mobility may depend on whether a targetTRP shares a signature sequence with at least one source TRP. Theability to perform RA-less mobility may also depend on whether a targetTRP has been provided a WTRU's DL data from the network to prepare forseamless handover.

A TRPG may have some common resources on which a WTRU served by at leastone TRP within the TRPG may use for UL transmission, possibly to any TRPwithin the TRPG. Such resources may be WTRU-dedicated, or may be TRP- orTRPG-dedicated. The resources may be included in an access table orsystem information for the TRPG. The resources may also be provided byat least one serving TRP.

A WTRU may also receive an indication of whether a grant provided in thesource TRP is valid in the target TRP. Such an indication may beprovided in the initial grant. For example, the WTRU may receive withthe grant a list of TRPs for which a grant is valid. It may also receivea translation rule or alternative resources to be used in a differentTRP if the WTRU decides to transmit in the UL following movement to adifferent TRP. An indication of a valid grant may also be provided inthe RAR, assuming the information about the pending grant was providedas part of the context transmitted in the RA message.

A valid grant may be indicated by resources in the target TRP whichreplace the resources in the source TRP. It may also be indicated by atranslation rule, which may be a frequency offset, time offset, ordifference in encoding, scrambling, or the like, which needs to be usedto derive the target TRP resources from the initially granted source TRPresources. A valid grant may also be indicated by a change in accessmechanism, protocol, or assumptions that need to be applied in thetarget TRP. A change may be, for example, new HARQ related parameters.

A WTRU may perform an UL transmission on such resources to indicate arequest for WTRU-autonomous HO. Some UL transmission parameters may bereused from at least one serving TRP, possibly only for the same TRPG.For example, UL timing advance and power control may be reused by theWTRU. UL transmission parameters may also be indicated, possibly withinthe configuration of common UL resources.

A WTRU may indicate the request for WTRU-autonomous HO in one or more ofthe following ways. The request may be an UL transmission on the ULresources dedicated for a WTRU. Such resources may be common for one ormore TRP within a TRPG. A WTRU may include preferred list of one or moreTRP identities (for example based on measurements) in the ULtransmission.

The request may be an UL transmission on the UL resources dedicated fora TRP. Such resources may be common for one or more WTRUs. A WTRU mayperform contention based transmission on those resources. A WTRU may beconfigured with plurality of TRP specific UL resources. A WTRU mayindicate the choice of target TRP by the selection of UL resourcesassociated with the target TRP. A WTRU may include a form of unique UEID to identify itself on the common resources.

The request may also be an UL transmission on the UL resources dedicatedfor a WTRU and TRP pair. WTRU may indicate the choice of target TRP andthe UE ID by the selection of appropriate UL resources reserved for theWTRU and target TRP.

The UL resources mentioned above may also be reserved for any ULfeedback transmission, including a CQI report, measurement report,scheduling request, possible WTRU-autonomous handover signaling etc). AWTRU may include type of report either in a MAC control element or mayimplicitly indicate the WTRU autonomous handover request by a choice aspecific signal or preamble.

The UL resources mentioned above may also be reserved explicitly forWTRU-autonomous HO request. Any WTRU transmission on the UL resourcesmay be considered a request for a WTRU-autonomous HO request.

In such an UL transmission, a WTRU may indicate its source TRP as wellas desired target TRP. Such indications may be explicit, or may beimplicit and depend on a parameter used for UL transmission. Parametersmay include a sequence used for demodulation reference signal or anorthogonal UL transmission resource. Others may also be used.

A WTRU may transmit a form of UE ID to identify itself to the targetTRP. A WTRU may use one or a combination of two or more of the followingto indicate the UE identity, for example, a unique radio levelidentifier (e.g. RNTI) allocated in the source TRP and/or a unique UEcontext ID that identifies both the source TRP, the WTRU context withinthe source TRP, a set of radio bearer or logical connection ID that maybe unique within a TRPG, and/or any transmission on the WTRU-specific ULresource may identify the WTRU implicitly. The WTRU may also include thecharacteristics of spectral operating mode and/or system signature usedto serve the WTRU in the source TRP.

In such an UL transmission, a WTRU may indicate its source TRP as wellas desired target TRP. Such indications may be explicit, or may beimplicit and depend on a parameter used for UL transmission. Parametersmay include a sequence used for demodulation reference signal, anorthogonal UL transmission resource, WTRU Buffer Status, or others.

A WTRU may provide an indication of WTRU-autonomous mobility to thesource TRP, in addition to information related to the target TRP. Suchinformation may be similar to that described for random access.

A WTRU may also provide WTRU information to the target TRP. Suchinformation may include for example, UL resources granted, HARQprocessing state, or WTRU contexts.

Such an UL transmission may also explicitly request reference signalresources from the target TRP to enable the WTRU to feedbackmeasurements. Such measurements reports may enable the addition of atarget TRP to a pre-existing set of serving TRPs, rather than simplyreplacing a source TRP with a target TRP.

A WTRU may restrict the autonomous HO procedure within the TRPG to whichthe serving TRP belongs. If a WTRU is served by more than one TRP,possibly part of two or more TRPGs, then WTRU may perform autonomous HOwithin the TRPs under all of those TRPGs. The TRPGs within which WTRUmay perform autonomous HO may be called serving TRPGs. A WTRU may applyadditional offset or bias towards TRPs within the serving TRPGs duringthe handover target TRP selection. A WTRU may perform L3 based handoverif the target TRP belongs to a non-serving TRPG.

A WTRU may also trigger autonomous HO by default towards all the TRPsirrespective of the TRPG they belong. A WTRU may be required to verifythe success of the autonomous HO based on the response from the network.For example, network may indicate the need to perform L3 based handovere.g. via a handover command message or L2 reset command, a WTRU may thenreset the L2 context, flush HARQ buffers and transmit a L3re-establishment message or handover complete message.

During or following the RACH procedure or WTRU-autonomous handover, aWTRU may send an indication to the source TRP that it has successfullyconnected to the target TRP. Such an indication may be used, forexample, to terminate data transmission and/or expected reception overthe resources of the source TRP. Specifically, in the case of the RACHprocedure, the WTRU may continue to receive/transmit data with thesource TRP following the transmission of the RA. The WTRU may then sendan indication to the source TRP of successful connection to the targetTRP, following which, it is assumed that data reception/transmissionwith the source TRP can be stopped.

The WTRU may send the indication to a source TRP of a successfulconnection to a target TRP at an instance of time, or when at acondition has been met. An indication of a successful connection to atarget TRP may be sent upon reception of an RAR from the target TRP. Anindication may also be sent upon reception of UL resources or DL dataobtained from the target TRP. An indication may also be sent uponsuccessful transmission/retransmission of any HARQ processes which wereongoing at the time the RA was transmitted, or the time autonomous HOwas decided. An indication may also be sent upon successful decoding andpossible reassembly by L2 (MAC, RLC, or similar layer) of a specific PDUor packet associated with a sequence number for which transmissions wereongoing when the RA was sent, or another specific sequence numberdetermined by the WTRU. An indication may also be sent upon theexpiration of a timer which may be started at transmission of the RA,reception of the RAR, decision to perform autonomous HO, or any otherevent following the aforementioned. An indication may also be sent Uponindication from the target TRP which may come in a RAR or at some finite(e.g. fixed or configurable) time following the RAR. The indication tothe source TRP may contain an identification and/or signature sequenceof the target TRP. The indication may also contain a status ofuntransmitted or unreceived PDUs at a specific L2 protocol layer. Theindication may also contain the latest TRP list maintained by the WTRU,or measurements of the target TRP.

WTRU context transfer is described herein. When performingmobility/handover, the WTRU context may be transferred to the new TRP.While in legacy systems this task was carried out by the network, in 5Gsystems this may no longer be the case. In such cases, the WTRU may beconfigured to transfer a portion of its context to a new TRP. This maybe motivated, for example, by a need to expedite handover when thetraffic requires it. Another motivation would be to reduce unnecessarybackhaul load. It may also lead to reduced number of transmissions andretransmissions as the WTRU HARQ information may be transferreddirectly.

The WTRU may thus be configured to transmit information to the new TRPwhen performing mobility/handover, in any order or combination. The WTRUmay transmit HARQ Related context. It may also transmit PDU HistoryInformation. The WTRU may also transmit Buffer Information. The WTRU mayalso transmit security information. It may also transmit RadioBearer/Logical Channel information and/or Source TRP information.

The WTRU may transfer the receiving-side and/or transmit side HARQcontext. This information may include, for each HARQ process configured,HARQ Process number/ID. The information may also include HARQ processstatus, wherein such statuses include terminated, on-going, number oftransmissions received/transmitted, new data, etc. The information mayalso include MCS/TBS or other control information of the packet beingreceived/transmitted on the HARQ process. The information may alsoinclude last feedback information transmitted/received, and/or timinginformation: including SFN for the last transmission of that HARQprocess.

This information may be used by the new TRP, for example, to determinethe exact state to continue transmission. More specifically, the new TRPmay determine the HARQ process status and continue transmitting wherethe source TRP left, provided the source TRP sends the HARQ context tothe new TRP as well. The WTRU context information may be used to ensurethat the new TRP is well in-sync to the source TRP.

The WTRU may transfer information regarding a history of successfullyreceived PDUs. Depending on the architecture, the PDUs may be RLC PDUs,PDCP PDUs or even MAC PDUs, or PDUs of a layer which carries a PDU countor number. For example, the WTRU may transfer information related to thelast successfully received PDCP PDU, or to the last NPDCP successfullyreceived PDCP PDUs. This information may contain, for example, thesequence number of the associated PDUs and additional informationrelated to the bearer or associated logical channel, for example.

This transfer of information relating to PDU history is designed toensure that the new TRP does not transfer PDUs that have been receivedsuccessfully already, which would waste resources, and ensures that noPDUs are dropped.

In order to expedite the start of the communication, the WTRU mayindicate to the new TRP its buffer status or information so that the newTRP may start scheduling the WTRU appropriately, or may reject thehandover in case the new TRP does not have sufficient resources for theWTRU.

The WTRU may further indicate, e.g. for URLLC traffic, the remainingtime for transmission of packet or packet segments. This remaining timemay indicate, for example, how long the TRP has to schedule the WTRU fortransmission before the latency requirement is violated.

In order for the WTRU to transmit and receive data securely to/from thenew TRP, security information may need to be transferred. Transmittingsecurity keys unprotected over the air may put the WTRU at risk of anattack. One option could be to use a special encryption key to actuallycipher the security context and transfer the ciphered security contextto the new TRP. The new TRP could use the special key to decipher theinformation. The special key could be, for instance, a public keypreconfigured in the WTRU or some other type of encryption key.

The WTRU may be configured to transfer Radio Bearer/Logical Channel(RB/LCH) information to the TRP. This information may be used, forexample, for the new TRP to determine the highest priority RB/LCH toschedule. This may be useful on the UL as the new TRP would not need towait to receive the configuration from the network and could startscheduling the WTRU without delay. This is particularly important fordelay-sensitive data streams e.g. for URLLC traffic.

The information transferred may include, for example, number of RB/LCH,for each RB/LCH, the associated ID, the QoS information such as latencyrequirement, bit rate, or reliability.

In order for a new TRP to fetch remaining WTRU context and to completethe handover procedure, it may be necessary for the new TRP to beindicated by the WTRU source TRP. This information may include, forexample, the source TRP ID, its IP address or other identifyinginformation.

In order for the new TRP to be aware of the current power-relatedinformation and state of the WTRU, the WTRU may need to transmit some ofthis information to the new TRP. This information may consist of, forexample, the latest power headroom computed by the WTRU, theinstantaneous power used for the last transmission or on a specificsubframe or set of subframes, the TRP specific power (if one exists) forthe source TRP, etc.

In order for the new TRP to be aware of the WTRUs currently configuredpower savings information in order that any WTRU-related state bemaintained, the WTRU may transmit its current power savings state aspart of the context. This may consist of the sleep cycle, periodicity,current DRX state, or any current values of the parameters maintained bythe WTRU which may have been known by the source WTRU and now needs tobe transferred to the new TRP.

A WTRU may provide some D2D-related configuration or information to thenew TRP, such as potentially the resource configuration, usage, sensingrelated information, and the like to the new TRP. This informationallows the WTRU to continue D2D related communication under the controlof the new TRP without interruption.

During mobility with multiple TRPs, a WTRU may communicate with multipleTRPs, either simultaneously, in TDM/FDM fashion, or based on certainrules which could depend on the TRP capability, the type of information(control vs data), and the type of data or service (e.g. logicalchannel).

A WTRU may also receive scheduling information from multiple TRPs. TheTRPs which may provide a single WTRU with scheduling that may furthercorrespond to the TRP list sent by the WTRU to the network. For example,a WTRU may report the TRPs for which measurements meet certain criteria.In response to such a report, the WTRU may be expected to receivescheduling from any of the TRPs provided in the report.

A WTRU may also be required to receive scheduling from a set of TRPs fora finite period of time, and receive scheduling from a possiblydifferent set of TRPs following this. For example, the WTRU may berequired to monitor control channels where such scheduling may bepresent. For example, the set of TRPs which may provide schedulinginformation may change periodically, or upon transmission of a new TRPlist by the WTRU. Upon successful reception of the TRP list by thenetwork, which may be accomplished through acknowledgement received bythe WTRU, the WTRU may assume that the list of TRPs which can providethe WTRU with scheduling may be changed to the transmitted andacknowledged TRP list. The network may also provide this listperiodically, and the WTRU may accordingly change the TRPs on which itis expecting scheduling information from.

A WTRU may be allowed to transmit simultaneously to multiple TRPswithout the need to send a RA or to perform a WTRU-autonomous mobilityprocedure described herein. Simultaneous transmission may occur usingdifferent antenna ports. The WTRU may also transmit in TDM, FDM, or CDM)fashion. These TRPs may coincide with the set of TRPs from which theWTRU receives scheduling.

These TRPs may also come from another, possibly independent, set ofTRPs. These TRPs may also coincide with the set of TRPs which are beingsignaled to the network in the TRP list. For example, the WTRU mayindicate to the network which TRPs it may transmit to in the uplink eachtime it sends the TRP list. A WTRU may also transmit two lists: a firstlist for the set of TRPs from which a WTRU desires to receivetransmissions, and a second list for the set of TRPs to which a WTRUwishes to transmit. A WTRU may also receive two lists from at least oneTRP: a first list indicating the set of TRPs the WTRU should monitor forpossible scheduling information, and a second list indicating the set ofTRPs to whom a WTRU may be expected (or allowed) to make ULtransmissions to.

For a given transmission, a WTRU may select the TRP on which to transmitto, based on a capability or service supported by a TRP (e.g. the typeof traffic supported). The TRP selection may also be based on availableTTI or set of TTIs supported by the TRP. TRP selection may also be basedon the TRP or a list of possible TRPs may be signaled to the WTRU for itto use (for example, as part of the UL grant). It may also be based on acurrent load of a specific TRP, which may be signaled by the network.TRP selection may also be based on an immediate or short termavailability of UL resources in that TRP. For example, a WTRU maytransmit SR on a specific TRP when the SR configured in that TRP occursfirst following the arrival of data in the WTRU required fortransmission. A TRP may also be selected based on transmit powerrestrictions, or the resources required (for example, specific TRPs maybe applicable only for specific numbers of antenna ports, PRBs, symbols,etc.).

A WTRU may be scheduled with resources for UL transmission and the WTRUmay select which TRP to transmit to. This selection may be made based onprior knowledge of the TRP capabilities, and the type of data which theWTRU wishes to transmit with the specific grant.

The WTRU may also be provided with the TRP for transmission in the UL aspart of the grant, either explicitly by identification of the TRP, orimplicitly by the specific TTI or resource set it signaled in the grant.

A WTRU may indicate to the network the TRP that will be used for ULtransmission. Such indication may be provided prior to the actual ULtransmission and may be provided to a single TRP (e.g. the Master TRPdescribed in more detail below) or to multiple TRPs (for example, to allTRPs in the TRP list, to all TRPs associated with a specific signature).Such an indication may be used, for instance, to allow the network toreuse specific resources in TRPs which are not being utilized by theTRP. The indication may be sent in a predefined resource, or in such away that it can be received simultaneously by multiple TRPs.

A WTRUs choice of a TRP to which to transmit UL transmission may bebased on capability information of the TRP which may be broadcast by thenetwork. TRP capability information may include possible TTIs which canbe used for UL transmission. Information may also include type oftraffic, logical channel priorities, or the like, which can betransmitted on this TRP. Capability information may also includeinformation relating to whether the TRP supports CP, UP or both types oftraffic. Capability information may also include maximum speed supportedduring UL transmission, or UL channels supported (e.g. PUCCH, SR, etc).

For example, a WTRU may be required to transmit L2 control information(such as MAC CE) only to specific TRPs based on their capabilityinformation.

A WTRU may identify, or be configured with a specific TRP which may actas the master TRP while the WTRU performs multi-connectivity withseveral TRPs. A WTRU may select and indicate the Master TRP to thenetwork. Such an indication may be part of the TRP list which isprovided to the network, whereby one of the TRPs would be designated bythe WTRU as the master. The Master TRP may be selected based criteriawhich may include: the TRP with the best measurements, the TRP locatedthe smallest distance from the WTRU, the TRP supporting all of theservices/capabilities required by the WTRU at a given time, the TRPindicating ability to act as a Master TRP, or the TRP providing the WTRUwith resources on which it may transmit Master TRP transmissionsindicating which TRP any specific UL transmission is for.

A WTRU may expect certain control-related communication to take placeonly with the designated master TRP. For instance, a WTRU may be allowedto transmit/receive L2 control information from/to the master TRP.

A WTRU may further be configured to perform mobility related actionsdescribed herein (transmission of the RA, procedures related toWTRU-autonomous mobility) when it decides to change the Master TRP.

Although features and elements are described above in particularcombinations, one of ordinary skill in the art will appreciate that eachfeature or element can be used alone or in any combination with theother features and elements. In addition, the methods described hereinmay be implemented in a computer program, software, or firmwareincorporated in a computer-readable medium for execution by a computeror processor. Examples of computer-readable media include electronicsignals (transmitted over wired or wireless connections) andcomputer-readable storage media. Examples of computer-readable storagemedia include, but are not limited to, a read only memory (ROM), arandom access memory (RAM), a register, cache memory, semiconductormemory devices, magnetic media such as internal hard disks and removabledisks, magneto-optical media, and optical media such as CD-ROM disks,and digital versatile disks (DVDs). A processor in association withsoftware may be used to implement a radio frequency transceiver for usein a WTRU, WTRU, terminal, base station, RNC, or any host computer.

1. A method performed by a wireless transmit/receive unit (WTRU) forhandover among a set of a plurality of coordinatedtransmission-reception points (TRPs), the method comprising: measuring afirst reference signal (RS) of a first set of the plurality ofcoordinated TRPs and a second RS of a second set of the plurality ofcoordinated TRPs; receiving a grant to transmit to the coordinated TRPs;transmitting to the first set of the plurality of coordinated TRPs; anddetermining, autonomously, whether to transmit to the second set of theplurality of coordinated TRPs rather than the first set of the pluralityof coordinated TRPs, based on the first RS, the second RS, and a changein circumstances.
 2. The method of claim 1 wherein performing themeasuring includes determining, for a signal received from at least oneset of the plurality of TRPs, at least one of: received power, receivedsignal strength, received signal quality, interference, or interferenceto noise ratio (SNIR).
 3. (canceled)
 4. The method of claim 1 furthercomprising: creating and transmitting a TRP list.
 5. The method of claim1 further comprising: receiving an indication of a master TRP.
 6. Themethod of claim 1 further comprising: indicating to a first TRP of thefirst set of the plurality of coordinated TRPs that a transmission wasmade to the second set of the plurality of TRPs.
 7. The method of claim1 wherein the WTRU provides WTRU-context to the second set of theplurality of TRPs.
 8. A wireless transmit/receive unit (WTRU) configuredto handover among a plurality of coordinated transmission-receptionpoints (TRPs), the WTRU comprising: a processor configured to measure afirst reference signal (RS) of a first set of the plurality ofcoordinated TRPs and a second RS of a second set of the plurality ofcoordinated TRPs; a receiver configured to receive a grant to transmitto the coordinated TRPs; a transmitter configured to transmit to thefirst set of the plurality of coordinated TRPs; and the processorfurther configured to autonomously determine whether to transmit to thesecond set of the plurality of coordinated TRPs rather than the firstset of the plurality of coordinated TRPs, based on the first RS, thesecond RS, and a change in circumstances.
 9. The WTRU of claim 8 whereinthe measuring includes determining, for a signal received from at leastone set of the plurality of TRPs, at least one of: received power,received signal strength, received signal quality, interference, orinterference to noise ratio (SNIR).
 10. (canceled)
 11. The WTRU of claim8 wherein the processor and transmitter are further configured to createand transmit a TRP list.
 12. The WTRU of claim 8 wherein the receiver isfurther configured to receive an indication of a master TRP.
 13. TheWTRU of claim 8 wherein the processor and transmitter are furtherconfigured to indicate to the first TRP of the first set of theplurality of coordinated TRPs that a transmission was made to the secondset of the plurality of TRPs.
 14. The WTRU of claim 8 wherein theprocessor and transmitter are further configured to provide WTRU-contextinformation to the second set of the plurality of TRPs.
 15. (canceled)16. A method for performing a random access procedure in a wirelesstransmit receive unit (WTRU), the method comprising: performing randomaccess procedures to a plurality of coordinated TRPs using the sameresources for each TRP; receiving at least one random access response(RAR); selecting one random access response of a particular TRP of theplurality of coordinated TRPs to continue the random access procedure,and storing the contents of the remaining access response; andcontinuing the random access procedure with the particular TRP.